You say your MIL is "extremely religious." I don't know what particular religious sect she embraces, but I think "legalistic" is more appropriate in her case than "religious." Just my opinion, as someone who reads the Bible on a daily basis, but in the New Testament Jesus was constantly at odds with the legalistic Phairasees who wanted to stick to the letter of the law and argue a point to death.
Why let her or anyone else make your lives hell? Don't hang around her. Your AH wants to see his mom so much, suggest he go to her house to see her. As far as you not mentioning another word, that is your right. Just think about it. You are boiling mad inside. You are not saying anything. Sounds like a loose canon on the deck, doesn't it? Keep venting here if you need to and vent to your sponsor.
So what if she's read the Bible a zillion times? People who HEAR what the message is saying don't get argumentative. They respect other people's right to freedom of choice to believe or not believe as they so desire. I could sit down and read the Koran and get into a spirited debate about what it says, but it doesn't make me a follower of Islam. Whatever she claims to be is her right, but as I recall Jesus said "I am gentle and humble of heart." Your MIL sounds about as gentle and humble as a steamroller!
Frankly, your AH is blowing smoke up your wazoo and you know it. Making him drink by not allowing his mom to come visit - oh, puuulleeeezzzzeeee!