Who, even writing children's fantasy, is Patricia A. McKillip still.
Periwinkle's father drowned at sea. Her mother is lost in her grief, staring out to see. Periwinkle herself works at the inn -- which is very busy when the king stays in his summer home, and still has to be kept neat by winter -- and lives in the hut of an old woman who vanished not long after her mother died. She starts to hex the sea in revenge, which is where the king's son, Kir, happens on her.
He gives her a message to give to the sea when she hexes it, and more consequences ripple outward. Involving a chained sea dragon. An old jealousy. A magician named Lyo who knows that periwinkles are flowers as well as snails. Fishermen finding strange catches -- after the few first get laughed at and told they mistook it, people stop laughing. Accidental magic.
As enchanting as ever her work is.