The Little Mermaid's Name is Luna

Luna is finally fifteen, and she is allowed to visit the surface, something she's wanted to do her whole life. But when she falls in love with Prince Charles after saving his life, she wants more than to see the humans - she wants to join them. To do this, she visits the Sea Witch, who will give Luna three days to convince the prince to marry her. She only asks one thing in return: Luna's voice. Luna agrees, and only then discovers that she faces death if she doesn't get the prince to love her. And when the Sea Witch interferes, her task is made impossible. Will she die and join the Daughters of the Air, who she sees in her dreams? Or will she convince the prince to marry her, despite the Sea Witch's spell?

Note: Cover is not mine. It's from Pinterest.