Having liked the book, Princess Academy by Shannon Hale, here are some other titles you might enjoy reading.
Once Upon a Marigold by Jean Ferris.
A young man with a mysterious past and a penchant for inventing things leaves the troll who raised him, meets an unhappy princess he has loved from afar, and discovers a plot against her and her father.
The Two Princesses of Bamarre by Gail Carson Levine.
With her adventurous sister, Meryl, suffering from the the Grey death meek and timid Princess Addie sets out to find a cure.