Daughter of the Bone Forest by Jasmine Skye
Rosy is a bone familiar, gifted with the power to shift into animals marked with exposed bone. She spends most of her days in the magical Bone Forest, caring for her feral grandmother and hiding her powers to avoid conscription by the Witch King’s army - until the day that she saves the life of Princess Shaw, a witch known as Death’s Heir. The princess offers Rosy the chance to attend the prestigious school, Witch Hall, as payment. There, Rosy finds herself embroiled in political games she doesn't understand. All she wants is to stay out of trouble until she can graduate and save her grandmother, but Shaw wants Rosy for her entourage, a partner to help lead the coming war. Will Rosy give in to her attraction for Shaw, or will the Bone Forest call her home once and for all?