Camp Princess 1: Born to Rule by Kathryn Lasky

Camp Princess is just like any other summer camp. Okay, so it's not exactly summer, since the magical kingdom of Palacyndra has seasons that change at the drop of a tiara. And it's not exactly camp, since the princesses stay in fully furnished turrets, complete with chambermaids. But it is a chance to get away from home and enjoy activities such as arts and crafts (with diamonds, of course) and moat swimming (bathing tiara required!). It's a place where Princess Alicia makes real friends, Princesses Kristen and Gunder-snap.

And for Alicia, Camp Princess becomes much more. A place of mystery. Her turret seems to be haunted, and the golden bird that she captured for the songbird contest refuses to sing a note! It's all utterly frustrating -- until one shadowy night, when Alicia feels a ghostly presence in her room and begins to discover a destiny far more exciting than anything she could have imagined.