Then in that case you should put the law down with your daughter. Her child is no angel either. She is like everyone else. An equal. Remind her of that. I too have family like that. If all five adults told her this maybe it could stop. Or maybe just not invite her to events with a lot of family members. This way your keeping peace with all the family members and your daughter. Separating her from the equation may take her out until she can get along with everyone. She also have mental Illness.