The summary could be:
A girl who is unhappy with her parents' split decides to live secretly in her school, where she breaks into lockers, cheats on exams, and exposes a teacher's drinking problem. She also asks out a boy who doesn't like her and hurts her best friend's feelings. She gets caught by the principal and the police and returns to live with her mom in a small apartment. She feels trapped and misses her freedom.
Here are some possible key facts extracted from the text:
1. The narrator's parents split up and she moved in with her dad, then her mom and her mom's boyfriend.
2. The narrator found a secret door in the school bathroom that led to a cleaning cupboard and decided to live there.
3. The narrator broke into various lockers, offices, and vending machines at school and stole food, tickets, and exam answers.
4. The narrator asked out Matt, a boy she liked, but found out he didn't like her back and her best friend Kimberly did.
5. The narrator wrote an anonymous note exposing Mr. Taylor, her science teacher, for drinking whiskey at school and got him fired.
6. The narrator got caught by the principal for breaking and entering and cheating on a math exam.
7. The narrator ran away to another town but turned herself in to the police the next day.
8. The narrator is now living with her mom in a small apartment and feels trapped.