Full-Level Mystic Heiress

Gabriella's adoptive parents throw her out of the house. A wealthy family then tracks her down, has the blood tie confirmed, and takes her in as the daughter they had lost. Gabriella has been hiding what she is. She is a master of the mystical arts, and once she is living with her birth family she stops acting the meek daughter and uses those arts in the open. Her adoptive family keeps coming back at her. An older cousin on the new side of the family resents her and works against her. There is also a danger to the family itself that stays hidden at first. She exposes what her adoptive family did, and she takes apart the cousin's plotting, and the household comes to treat her as one of their own. She decides she will protect them. At that point the man who has been behind the trouble shows himself, and the family's problems go on from there.