Sammy Keyes Mysteries

From author Wendelin Van Draanen's website: 

The first of the Sammy Keyes mysteries introduces the spunky heroine and her cast of friends, family, and enemies in a race to catch a thief before he finds her.  Sammy negotiates living illegally in a seniors-only apartment complex with her grandmother, navigates the minefield of middle school (including mean-girl Heather Acosta), and infiltrates the seedy Heavenly Hotel to get to the bottom of a burglary she’s witnessed.