Hi, I'd like to help you with your question.
It sounds like your husband needs to step in and deal with this. It is his mother and he is responsible for dealing with her. She should not be coming into your home and criticizing you. She is not respecting your home, you or your family.
By your husband leaving you to deal with this situation, it has gotten out of hand. He should sit down with his mother and tell her that she is to respect him and his family. Then he needs to set rules for her to follow such as calling before she comes over, respecting his family and not criticizing anyone while she is visiting. He should reiterate that she is a visitor and not there to tell you what to do. This should come from him and him alone. Otherwise, if he tells his mother you asked him to deal with her, his mother will only blame you and dismiss what is being said. And it will cause more conflict.
Once your husband talks with his mother, have him be sure she follows through with the rules. If she breaks rules, then he is to remind her again. Do not step in and do this yourself. She needs to be dealt with in a firm and direct manner. Keep emotions under control and do not point fingers. If she tries to pick a fight, leave. If she is in your home, ask her to leave. Keep doing so in a firm manner until she does leave.
If she shows up unannounced, consider stopping her at the door and telling her that you are busy and can't see her at that time. Do this anytime you feel you do not want to deal with her. It is your house and your right to have some privacy. If she has a key, change your locks.
Eventually, she will learn the boundaries your husband sets for her. She will also have to learn to respect you and your family and vent her frustrations in another way.
I hope this has helped you,Kate