Don't know if that's the real question. Might it be, is her dad too attached to his daughter? All kids will sleep with their parents as long as they are allowed. He's the adult, not your daughter. He needs to understand parenting is taking a little person uncapable of doing anything for themselves and gradually, over about 20 years transferring complete control of their life over to them. If he wants a 20 year old incapable of standing in her own two feet, he's off to a great start.