Four sisters novels

Princess Aislynn's magical ability is powerful and uncontrollable, so she is "redirected" into the order of Fairy Godmothers, where her heart is removed and stored in a hidden cabinet, and she must spend the rest of her life devoted to serving another royal family--but her growing friendship with a palace gardener causes Aislynn to question the vows she has taken, and the motives of those who would prevent her from "straying" from the path.