Twisted Roots by Virginia Andrews
From the outside, Hannah Eaton, Willow De Beers' teenage daughter, lives a charmed life in wealthy Palm Beach, Florida. But deep inside, she is miserable and lonely. Her mother and stepfather have a sickly new baby which takes up all their attention. Her father isn't so sure that she's his child. Her crazy Uncle Linden is the only relative who has time for her. And her new boyfriend, sexy guitar player Heyden Reynolds, has a troubled family of his own. Together, Heyden and Hannah decide to run away to New Orleans, where they stumble onto a rundown old farmhouse and a woman who is convinced Hannah is her long-lost daughter. At first the charade seems like a kindness, but then things spiral out of control . . .