Jace is a street girl, and has been for 2 years. She ran from her foster parents when she was 12, and never looked back. Jace was doing well, living anonymously as a boy until the spaceship crashed into Big Ben. And then everything changed when the Doctor found her. He gave her a home.
Rose is starting her new life with her new Doctor. She has to get used to doing the ordinary instead of traveling the stars in the TARDIS with the Doctor she used to know.