She was just 8 years old when her father was drafted. The day he left was the day she entered the Academy. Her mother cried when they took her. She was her mother's only daughter. She was her youngest. They had taken her son as well, her daughter's older brother, Theta.
Her son had ran off as soon as his TARDIS was ready. He was no longer a part of their family. Seeing that he hadn't returned home from his first mission.
Then 3 years ago before the madness, the Council brought him back. They had forced him to regenerate. She had been forced to watch his punishment. She had cried as she listened to her son's screams. After regenerating he had been sent back to Earth.
Her son was now lost to her. Her daughter would be next, if she didn't do something about it. So during a time when she was allowed to see her daughter, the mother, kidnapped the daughter and hid her.
Now her daughter was 11 years old. Her son who had been called back to the planet was at least 400 years old.
With in days the Time War had started.
She was running out of time. She needed a TARDIS. After locating one and after setting a course to a place that her son had secretly told her about, the mother told her daughter how to pilot the TARDIS in case of an emergency, the two shared tearful good bye. The mother whispered something in her daughter's ear. After this trip, her daughter wouldn't remember her life on Gallifrey and her family. The TARDIS would sacrifice itself after letting her daughter out.
During the trip however, the TARDIS got snagged in a crack in time, taking her passenger to a different reality. A reality where Time Lords and Gallifrey weren't real.
It all worked out in the end though. A couple in Fordwich, Kent, England, found the small 11 year old girl in the small park near their home.
The girl didn't remember how she got there nor could she remember her name. She did however tell them her age.
The couple who had found her would name her Lexi Finn. They didn't give her a middle name. That name would come to them later.