Mil threatening with attorney over cosleeping

I need advice on how to handle my mil. She is always telling us we are unfit parents. She doesn't agree with us cosleeping. Yes there is controversy on the subject but it is not neglectful. She has mentioned talking to an attorney and only not going through with it because dh says not to. It doesn't stop there though. She is constantly in our business. My son has a doc appointment coming up and mil says she'll take him and we don't need to be there. Um excuse me...I'm close to going off on this lady.