Lake Of Spirits by Keith Robinson
"So that's it for her?" Simone said, unable to contain the wave of bitterness. "She's one of the lost?"
Jolie was just a one-year-old baby, part of an experimental shapeshifter program in Simone's world, when she turned into a jengu (one of the miengu water spirits) and stuck in that form. Faced with raising a creature they knew little about, the scientists had no choice but to hand Jolie over to others of her kind, the mysterious people of the lake.
Sixteen years later, Simone is busy introducing the next generation of shapeshifters to their new home. Hal and his friends are settling in at school when it occurs to Simone that, with the help of Abigail's little glass faerie ball and its ability to unlock deep-seated memories and abilities, she might be able to bring Jolie back into the human world. It's said that the miengu can heal the sick, and Jolie would be an invaluable asset to have around - that is, if her enchanting beauty and mischievous ways don't escalate into disaster.
This is a tale of paranoia, betrayal, and impending doom. Like sirens luring ships onto rocks, Jolie seems sweet-natured at first... but Hal and his friends slowly discover that there's more to her than meets the eye. Can they figure her out before the proverbial ship smashes itself to bits?