The Changeling Sea

The sea has taken everything away from Periwinkle; it has drowned her fisherman father and left her mother barely able to cope. So Periwinkle, a chambermaid at the inn of a small fishing village, decides to hex the sea. It works surprisingly well, disrupting the sea queen's magic. A chained sea monster appears from the depths, and the king's melancholy son, Kir, nearly drowns trying to get to the country under the sea. With the help of the magician Lyo, Periwinkle uncovers and reverses the sea queen's curse.

Synopsis from Open Library.