She is perhaps the most mysterious and enigmatic member of the team, so not much is known about Parker's Leverage backstory. Like all the Leverage characters – her fellow criminals especially – information about Parker's life is mostly revealed in bits and pieces throughout the run of the show, often via flashbacks. Unlike most of the characters, however, there aren't many episodes dedicated to revealing more about her life before joining the Leverage team. Plus, only one person from Parker's past before Leverage has ever appeared.

https://screenrant.com/leverage-parker-backstory-known-before-join-team/