Nikki A.S.H. received a tryout with WWE in London during the autumn of 2015, and in April 2016, she was one of ten signees that had begun training at the WWE Performance Center in Orlando, Florida. She debuted for NXT on April 22, during a live event. She made her first televised appearance and in–ring debut on the August 17 episode of NXT under the name Nikki Glencross, where she competed in a six-woman tag team match along with Carmella, and Liv Morgan, defeating Daria Berenato, Mandy Rose, and Alexa Bliss.
On the 12 October episode of NXT, Nikki returned under the name Nikki Cross and as part of the debuting heel stable, Sanity, along with Alexander Wolfe, Eric Young, and Sawyer Fulton (who was later replaced by Killian Dain). She and Young accompanied Fulton and Wolfe for their winning effort against Bobby Roode and Tye Dillinger in the first round of the Dusty Rhodes Tag Team Classic. One week later, Cross scored her first televised singles victory over Danielle Kamela, however, the decision was reversed when Cross continued to attack Kamela after the match.
On the 11 January 2017, episode of NXT, Cross came to the aid of NXT Women's Champion Asuka, who was being attacked by Peyton Royce and Billie Kay, before turning on Asuka and attacking her as well. As a result, Cross, Royce and Kay were placed in a four-way match at the NXT TakeOver: San Antonio event on 28 January, which Cross failed to win. In May, Cross participated in a number one contender's battle royal for Asuka's NXT Women's Championship, where she, Ruby Riot, and Ember Moon were attacked by Asuka for being the last competitors left in the match and as a result, all four of them were placed into a four–way championship match at NXT TakeOver: Chicago, which was later changed to a three–way match after Ember Moon suffered an injury. At the event, Cross failed to capture the title. In a rematch which was contested in a three–way elimination match once again against both women, Riot was the first eliminated before the match ended in a no contest as Cross and Asuka brawled backstage. This led to a last woman standing match (the first ever in WWE history) between the two women for the NXT Women's Championship on the 28 June episode of NXT, in which Cross was once again defeated. On 19 August at NXT TakeOver: Brooklyn III, Cross accompanied and helped Sanity to capture the NXT Tag Team Championships from The Authors of Pain. In October, Cross earned herself a spot for the fatal four–way match for the vacant NXT Women's Championship at NXT TakeOver: WarGames on 18 November, which was ultimately won by Ember Moon.
In early 2018, Cross began a little winning streak, defeating Lacey Evans and Vanessa Borne. During the 2018 Superstar Shake-up her fellow stable partners Eric Young, Alexander Wolfe and Killian Dain were drafted to SmackDown, leaving Cross on NXT to work again as a singles competitor. Throughout the summer, Cross started a feud with Shayna Baszler over the NXT Women's Championship, which led to a match between the two, in which Cross was once again unsuccessful and was defeated by technical submission. After a short hiatus, Cross returned in August and she was placed in the Aleister Black attack storyline where she was revealed to be a witness as she was on the roof of the building at the time he was attacked. In September, Cross also started a short feud with Bianca Belair which led to a match between the two that ended in a double count–out. One month later, on the 17 October episode of NXT, a rematch ended in a no contest, after Aleister Black returned and interrupted it to ask Cross who his attacker is. Johnny Gargano was eventually revealed as the attacker and her involvement in the storyline sparked a match between Cross and Gargano's wife Candice LeRae, whom she was able to defeat in a singles match at NXT TakeOver: WarGames. Cross wrestled her final match on the 9 January 2019 episode of NXT, where she lost to Bianca Belair, officially ending the feud between the two as well.
On the November 6, 2018 episode of SmackDown from Manchester, England, Cross made her surprise main roster debut by answering an open challenge from WWE SmackDown Women's Champion Becky Lynch, who defeated her in a non-title match. On the December 17, 2018 episode of Raw, Cross was advertised as one of the six NXT wrestlers about to be moved to the main roster. On the January 14, 2019 episode of Raw, Cross made her Raw debut, teaming with Bayley and Natalya in a winning effort against The Riott Squad (Liv Morgan, Ruby Riott and Sarah Logan).
At the Royal Rumble, Cross entered her first Royal Rumble match at number 8, lasting nine minutes before being eliminated by the IIconics (Billie Kay and Peyton Royce). On the February 4 episode of Raw, Cross and Alicia Fox were defeated by The Boss 'n' Hug Connection (Bayley and Sasha Banks) in a match to determine the final Raw entrants in the tag team Elimination Chamber match to determine the inaugural WWE Women's Tag Team Champions at the Elimination Chamber event. On April 8 on Worlds Collide, she took part in a triple threat match for the NXT UK Women's Championship won by defending champion Toni Storm.
After not being mentioned during the 2019 WWE Superstar Shake-up, Cross was confirmed to have been drafted to the Raw brand on the May 8 taping of Main Event (aired on May 11). After weeks without appearing on Raw, Cross returned on May 13 in a backstage scene with Alexa Bliss; this marked a change in her character, who appeared calmer and more collected than during her time in NXT. In the segment, Cross, seemingly sad and claiming that nobody even noticed that she had joined Raw, appeared to bond with Bliss, whose ring gear had been lost, and accepted to fill in for her in her upcoming match; Cross won her match later that night, a fatal four-way match against Dana Brooke, Naomi, and Natalya. This was her first match on Raw since February. She later unsuccessfully took part in the Money in the Bank ladder match at the Money in the Bank event, having replaced Bliss who suffered an injury. After the event, Cross, having become Bliss' "best friend", started acting as her manager and tag team partner, starting on the May 19 episode of Raw during which she, Bliss and Becky Lynch defeated Lacey Evans and the IIconics.
On the June 17 episode of Raw, Cross and Bliss faced the IIconics for the WWE Women's Tag Team Championship (Cross' first title opportunity on the main roster), but were unsuccessful due to a distraction by Bayley, who was also in a feud against Bliss for Bayley's SmackDown Women's Championship; Cross, very upset by the loss, asked Bliss to be in her corner at Stomping Grounds, where Bliss would challenge Bayley for the title. Bliss was unsuccessful at the event; during the match, Cross, still upset at Bayley, had tried to attack her, which she subsequently believed to be the cause of Bliss' loss. Two days later, she appeared on SmackDown asking for another title opportunity for Bliss; she then defeated Bayley in a non-title match, earning Bliss another match for the title at Extreme Rules. Cross made the match at Extreme Rules a handicap match for Bayley's title where she teamed with Bliss in a losing effort. On the August 5th edition of Raw, Bliss and Cross captured the WWE Women's Tag Team Championship, marking Cross' first championship in WWE. The duo successfully retained the titles at Clash of Champions against Fire & Desire (Mandy Rose and Sonya Deville) the next month. She and Bliss lost the titles at the Hell in a Cell event, to the Kabuki Warriors, after Asuka used green mist on Cross.
Although drafted separately instead of as a team during the 2019 WWE Draft, Cross and Bliss remained on Raw, but the team was then traded to SmackDown. Cross made an immediate impact on the brand, winning a match to earn a future shot at the SmackDown Women's Championship. On the November 1 episode of SmackDown, Cross unsuccessfully challenged Bayley for the SmackDown Women's Championship due to interference from Sasha Banks. A week later on the November 8 episode of SmackDown, Cross lost to Banks via submission. Cross then announced that she would be on Team SmackDown at Survivor Series along with Banks, Carmella, Lacey Evans, and Dana Brooke. At Survivor Series, Cross was the first woman to get eliminated and Team SmackDown would go on to lose the match. On the SmackDown after Survivor Series, Bliss would return and save Cross from an attack by Fire 'n' Desire after Cross defeated Mandy Rose. On the July 31, 2020 episode of SmackDown, Cross showed signs of a heel turn by shoving Bliss after the match against Banks and Bayley.
As part of the 2020 draft in October, Cross was drafted to the Raw brand. She had a short feud with Alexa Bliss but was defeated both times. She was then absent from television until the May 13, 2021 episode of Main Event, where she defeated Naomi. On the May 17 episode of Raw, she appeared as the only female In the lumberjack match between Damian Priest and John Morrison. The next week on Raw, she defeated Rhea Ripley in a Beat the Clock Challenge match. On the June 21 episode of Raw, Cross debuted a new super hero gimmick called Nikki A.S.H. (Almost a Superhero), and she teamed up with Alexa Bliss to defeat Nia Jax and Shayna Baszler in a women's Money in the Bank ladder match qualifier after rolling up Baszler.. At Money in the Bank, Nikki A.S.H. won the women's Money in the Bank ladder match. The following night on Raw, she cashed-in her Money in the Bank contract and defeated Charlotte Flair to win the Raw Women’s Championship for the first time in her career. At SummerSlam, she dropped the title back to Flair in a triple threat match, also involving Rhea Ripley, to end her reign at 33 days. Nikki then teamed with Rhea Ripley to defeat Nia Jax and Shayna Baszler. Nikki and Rhea then defeated Tamina and Natalya to become number one contenders for the Women’s tag team Championship. On the September 20 edition of Raw, they won the WWE Women's Tag Team Championships. However, on the November 22 episode of Raw, they lost the titles to Carmella and Queen Zelina, ending their reign at 63 days.
On the January 3 episode of Raw, they failed to regain the titles from Carmella and Queen Zelina in a rematch. The following week, Nikki would turn on Ripley after issuing a challenge to Queen Zelina and Carmella for the Women's Tag Team Championships, ending Super Brutality and turning her heel in the process. She participated in the Royal Rumble match at the namesake event and entered at number twenty-two, eliminating fellow superheroine Mighty Molly due to being jealous of her, before she was eliminated by eventual winner Ronda Rousey. At Elimination Chamber, she entered the Elimination Chamber match for a Raw Women's Championship match at WrestleMania 38, but was eliminated by Ripley. On the May 2 episode of Raw , she would win the WWE 24/7 Championship, only to lose it to Dana Brooke later that night. The following week on Raw, A.S.H. and Doudrop challenged the WWE Women's Tag Team Champions Naomi and Sasha Banks in a non-title match, but they were unsuccessful. After the Women's Tag Team Championship was vacated on May, Nikki and Doudrop entered a tournament to crown new champions, which began in August; they lost in the first round to Alexa Bliss and Asuka. On the August 26 episode of SmackDown, Nikki and Doudrop entered a second chance fatal four-way match to return to the tournament among three other teams, which was won by Natalya and Sonya Deville. On the August 30 episode of NXT 2.0, A.S.H. and Doudrop made a surprise appearance as they challenged NXT Women's Tag Team Champions Katana Chance and Kayden Carter for their titles at Worlds Collide. At the event, Nikki and Doudrop were unsuccessful.
On the October 24 episode of Raw, Cross interfered in a match between Bayley and Bianca Belair, attacking both women, and reverting back to her “crazy” gimmick and the Nikki Cross name. On the November 7 episode of Raw, Nikki joined Damage Control (Bayley, Dakota Kai, and Iyo Sky) in a brawl against Bianca Belair, Asuka, and Alexa Bliss. Later in the night, Nikki defeated Dana Brooke to win her eleventh 24/7 Championship, but later threw it into a trash bin backstage. This would officially deactivate the title, with Cross becoming the final champion with her final reign ending at one day. Cross then briefly began a storyline where she stalked Candice LeRae. Cross teamed with Natalya against Chelsea Green and Piper Niven on the October 23, 2023 episode of Raw, but just stood by the ring, making no effort to take part in the match before walking off. Cross spent the next few months in a similar state, making no attempt to fight when involved in matches and mainly being seen wandering backstage areas.
Cross was included as part of debuting The Wyatt Sicks stable on the June 17, 2024 episode of Raw, appearing visually to represent Sister Abigail from Bray Wyatt's Firefly Funhouse, a character previously a part of Wyatt's history and lore.