The Girl from the Sea (Relié)

Fifteen-year-old Morgan has a secret : She can't wait to escape the perfect little island where she lives. She's desperate to finish high school and get as far away as possible from her sad divorced mom, her volatile little brother, and her group of best friends - who don't actually know Morgan at all. Because really, Morgan's biggest secret is that she has a lot of secrets, including the one about wanting to kiss girls.
Then one night, Morgan is saved from drowning by a mysterious girl named Keltie. Suddenly, life on the island doesn't feel so stifling anymore. But Keltie has some secrets of her own. And as the girls start to fall in love, everything they've each been hiding will find its way to the surface, whether Morgan is ready or not.