Hi , A. ...
Wow , this is a tough one. (( Hugs )) to you and your family.
BUT - as tough as it is , your mother needs to respect your boundaries. You also have to set them , make them known , and enforce them. This means , even if she gets mad , throws a fit , or stops speaking to you for a few days , you MUST be firm with her. You don't have to be rude or cause a big scene - just , " Mom , I am handling this situation with my daughter - these are OUR rules for OUR daughter ; OUR marriage , and that's it ... we are doing this our way. " And then stick to it.
A. , if you don't do this now , you'll regret it. It's very important to make your boundaries known. If your mom cannot respect them , it's her problem , and you need to let it BE her problem.
If I may , I'd like like to suggest a book : it's called " Boundaries " by Dr. Henry Cloud and Dr. John Townsend.
I , myself , am reading it and we bought copies of it for people we love. It's an EXCELLENT book because a lot of people have problems with boundaries.
Good luck and God bless. It takes a lot of effort and bravery to change things like this in families.
~ A.