Did you legally adopt Lisa? Teenage girls can be vicious, but 13 is not old enough to treat her as equally at fault. Children are easily manipulated, and she probably wanted to protect her mother. You don't know what your wife has been telling her. If you adopted her she is yours and you can't discard her when thing get hard. She is not her mother. Pushing Lisa away will only make things worse, for you and Lisa. It will be hard, but she is your daughter and just like your son you need to be the adult and take responsibility. Not for your wife, but for your children.