Princess of the Wild Sea by Megan Frazer Blakemore
Princess Harbor Rose is cursed. She's lived her whole life hidden away on a remote island with her magical aunts, following all the rules for being a princess. Now it is only one more year until thirteenth birthday, when a hero will finally arrive to save her from her curse.
But as with any story, there are two sides . . . and the curse told of much more than a single princess's uncertain fate. It told of a dangerous foe rooted in powerful magic. It told of a terrible war that could destroy everything if a young hero didn't arrive in time. It told of a magic imbued with hope that could save everyone, but only if they believe.
With her beloved kingdom and island at grave risk, Harbor Rose has a choice: Should she wait for the hero, or take matters into her own hands?-Goodreads