So.... I have a stepchild my MIL has helped raise from the moment she was born, when I came into the child's life, I was constantly told I wasn't her mom by my MIL.. 

fast forward 8 years later. We now have a 4 year old (she's 12) I have found out she's touched my son, inappropriately, as well as forced him to make out with her. My MIL quickly placed blame on our household. Shits a whole show.