In those files, she found information about the facility she was kept at and subsequently escaped from when she was young, and it's there that she wants to go, to resolve things.
Part of your deal with her to get her onboard was to allow her to go through any file she wanted.
Jack was experimented on, tortured and regularly mistreated as a youth, and a result, she has both incredible biotic powers, and an immense chip on her shoulder. She tells Shepard about her past, her childhood locked up in a Cerberus facility. Speak with her, and she'll let the Commander know that she has a bit of a problem. There, amongst the ship's engineers, you'll find Jack nestled away by herself. To begin this quest, you'll need to head to the bowels of the Normandy, to the very lowest level.
