What's the best way to tell your mother-in-law to stop fucking your kids up?

I've already told my mother in law that her trying to parent my kids really bugs me but she still hasn't stopped. Most recent example would be me telling my six year old to figure out her math homework and Grandma swoops in at the sound of her whine and tells her the answers. Now she pretends to be dumb and whine till grandma saves her... via /r/Parenting https://ift.tt/2qP14up