I’m sorry but if I had a MIL like you I think I’d feel the same way. I realised that when I read your first sentence. “ I do everything for my son and DIL....”
You should not be doing everything for them. They are adults and as such should not have an interfering MIL buying a bath mat when theirs goes straggly for eg. Get real, give them some independence and space to lead their own lives for heaven sake. I would say it’s not a question of what you do with her but what she does with you! You’ve already caused friction between your son and DIL. If you truly loved your son and grandchild you would be letting them live their lives the way they want to and be happy for them. What sort of example are you setting as a supportive grandparent? You should only give advice if asked for it. If you were my MIL I would be having nothing to do with you until you got off your high horse and lowered yourself to make a ....genuine apology..... and .... back off!!
Please help! (grandchild being locked in bedroom)



