Sammy Keyes and the Hotel Thief by Wendelin Van Draanen
This is the first book to a kids mystery series starring super sleuth Sammy Keyes. Sammy lives illegally with her grandmother in an old folk's home, her mom is a flake who's abandoned her to pursue the Hollywood dream. While spying on neighbors with her binoculars, young Sammy catches sight of a robbery in the Heavenly Hotel across the street. With plenty of sass and gumption, she follows clues to discover who the thief is and along the way is met with obstacles from mean Officer Borsch and Heather the bully from school.