Fairest by Gail Carson Levine
Once upon a time, all she ever wanted was to be pretty...
The fairy Lucinda has once again given a dreadful gift. This time it's a mysterious magical mirror. The gift is disastorous when it falls into the hands of Aza, who never looks in a mirror if she can help it. In the Kingdom of Ayortha, Aza is most defintely not the fairest of them all. Many spurn her. Many scoff at her. She keeps out of sight.
But in the land of singers, Aza has her own gift, one she's come by without fairy intervention: a voice that captivates all who hear it. In Ontio Castle, merry Prince Ijori is drawn to it, and Queen Ivi wants too use it to her own ends. Queen Ivi would do anything to remain the fairest in the land.
From a new tale of the author of Gail Levine...this one will surely be the fairest among all.