The Princess and a Test of Power by Brittany Fichter

A lost princess seeking shelter.
A prince cursed to solitude.
A test to find the one with the power to restore him.

After being touched by a malevolent power, Prince Phillip has slowly been losing his ability to communicate. But his older sister, Lady Freya, is determined to see her little brother take his rightful place on the throne–and she has a scheme to do it.
All she must do is find the lost princess of the ancient Bianne line and get them to fall in love. She even has a test with which to find the girl.
Lady Freya’s only problem? The entire Bianne family was murdered over a decade before, and their island of healing was destroyed with them. Rumor has it, however, that the youngest princess survived. And just when Lady Freya is about to lose all hope, a shoeless, impoverished young woman comes knocking at the castle door…