Tidal by Amanda Hocking book 3 in the Watersong Series

Blurb: Her only hope lies with her greatest enemies. Gemma is facing the fight if her life. Cursed by beautiful but deadly sirens,  her extraordinary powers have a terrifyingly dark side, and becoming human once more is proving her greatest challenge yet. As she struggles to break the curse, the sirens, Penn, Lexi and Thea,…