Andrea Lee's first opponent in her Invicta FC debut was Shannon Sinn, a fight in which she won by unanimous decision. Andrea's next opponent was the more experienced Roxanne Modafferi, who defeated her in a close split decision. Lee bounced back by defeating Rachael Ostovich at via armbar submission with seconds left in the fight. Lee then fought for Legacy FC where she defeated Ariel Beck to become the Legacy FC Flyweight Champion. In 2016, Lee fought again for Invicta where she was submitted by Sarah D'Alelio. She was subsequently suspended for nine months due to a positive drug test for a diuretic. Lee would make her return to Invicta at the beginning of 2017 with a quick knockout victory over Jenny Liou. The following month, she defeated Heather Bassett to become the inaugural LFA women's flyweight champion. Lee followed up with a decision win over Liz Tracy in Invicta and a successful LFA title defense over Jamie Thorton in her fourth fight of the year.
Ultimate Fighting Championships
In September 2017, Lee signed with the UFC initially to make her promotional debut just two weeks after her last fight. She was expected to face Kalindra Faria at UFC 216 but within hours of the bout announcement she was pulled from the card due to a clause in the UFC Anti Doping Policy which requires fighters with prior violations to serve a 6-month period in the testing pool prior to competing. Lee faced Veronica Macedo on May 19, 2018 at UFC Fight Night 129. She won the fight by unanimous decision. This win earned her the Fight of the Night bonus. Lee was expected to face Jessica-Rose Clark on December 15, 2018 at UFC on Fox 31. However, Clark was forced out of the bout as she was hospitalized due to weight cutting issue and deemed medically unfit to compete by UFC physicians. As a result, the bout was cancelled. Lee faced Ashlee Evans-Smith on February 17, 2019 at. She won the fight by unanimous decision. Lee faced Montana De La Rosa on June 22, 2019 at UFC Fight Night 154. She won the fight by unanimous decision. Lee faced Joanne Calderwood at September 9 at UFC 242. She lost the fight via split decision. Lee faced Lauren Murphy on February 8, 2020 at UFC 247. She lost the fight via controversial split decision. 12 out of 12 MMA media outlets scored the contest for Lee with none scoring it for Murphy. Lee is scheduled to faced Roxanne Modafferi on September 12, 2020 at UFC Fight Night 178.
Lee's moniker, KGB, was given by her coach as he thought she looked like a Russian. On one occasion at the Muay Thai World Championships, where Lee secured a victory, the entire Russian team approached her to have pictures taken due to the "KGB" patch on her trunks. A police report was filed on August 5, 2018 concerning an abuse by Lee's husband, Donny Aaron. Aaron, who created controversy with his Nazi tattoos, was arrested and jailed on May 30, 2019 after nine months on the run, for domestic violence and false imprisonment after burning Andrea with a cigarette and choking her.
