Sorry to read that your mother is a dolt when it comes to your feelings. Sadly this is not unusual for family.
Your husband sounds like a wonderful person to be able to handle this as well as he does. Ma is pushing your buttons for some reason that we do not know.......maybe she doesn't even know?!
You are an adult and you don't have to see anyone you don't want to. Your husband adopted your children making them yours (together......btw that was awesome of him to do) and your family is whole and complete. 'Cept ma.
Somehow you will have to decide how you're going to handle your mother in a more stern fashion. She hasn't listened to your requests over the years and continues to do this. She isn't gonna stop now.
Work with someone you trust on practicing statements you can use on ma to shut her down in her tracks next time she even attempts to launch into the ol ex and in laws song and dance. Cut her off before she begins.
I don't have any practicals as to how to go about this but I do have lots of support for growing stronger so that you will be able to enforce this boundary with your mother.
You deserve to not have this fuss in your life.