Mermaid moon - Susann Cokal

From the author of the Michael L. Printz Honor Book The Kingdom of Little Wounds comes an original fairy tale of belonging, sacrifice, choice, hope, magic and mortality.
This is just a children's tale; would you wreck your ship for it?
Would you drown for a mere mother's story?

Sanna is a mermaid - except her mother was landish, not seavish. The undersea witch who delivered her cast a spell that made her people, and her mother, forget her birth. Sanna longs to find her mother so much that she apprentices herself to the witch, learns the magic of making and unmaking, and fashions herself a pair of legs to go ashore on the Thirty-Seven Dark Islands, the nearest anyone can remember to where they left her mother. There, Sanna stumbles into a wall of white roses and a community desperate for a miracle - and into a baroness who would do anything to live for ever.