The river has teeth
(Book)

The car Natasha's sister was driving was found abandoned on the edge of a local nature preserve known as the Bend. Della's family has channeled magic from the Bend for generations, providing spells for the desperate. When Natasha turns up on her doorstep, Della knows it will take more than a potion to help her. She's hiding a secret: the beast responsible for the disappearances is her own mother, who was turned into a terrible monster by magic gone wrong. Now they are each other's only hope. -- adapted from jacket