Sammy Keyes and the Hotel Thief by Wendelin Van Draanen
Sammy Keyes must be a magnet for trouble...
I mean it's bad enough that she has to live illegally in a seniors-only building with her grandmother while her mother tries to make it as a move star. And worse that she witnessed a burglary in progress--and that the theif saw her. And worse still that nosy neighbor Mrs. Graybill is onto her, and that the thief is after her. But on top of all that, she also manages to make an enemy of the queen of mean at her new school and get suspended on the first day.
Welcome to the wild world of Sammy Keyes!