It's really her problem. Don't trust her. Be polite but keep your emotional distance. I'm not surprised at your husband's response since he can't do anything about her and doesn't understand her motives.
I would really try not to take her attitude personally. She probably treats anyone who marries into the family that's not "just like her" like this. And the fact is that you could change things about yourself... become Catholic even... but it wouldn't make her happy or nicer because you don't let her cow you down. She doesn't scare you and you don't bend over backwards to make her happy. Of course she's hot and cold with you.
My best advice with this snooty self-involved "lady" would be to limit your interactions with her and ignore her texts unless there's an emergency. Instead of letting her anger you, look for the humor in how insecure you must make her feel. Look at the effort she goes to in order to make you trust and like her and then once that trap is set she "puts you in your place."
So yes, I've been through this with some of my husband's aunts. I get along with them much better since I stopped playing their games on their terms. :-)