You need to stop trying to talk to her about this. Let it happen only at the MC office. At least then there is a referee. Next time, if you disagree with her, say so. Not an argument, but a calm thoughtful statement. The WAS does re-write the history of the marriage to justify her actions, so she is going to see it differently. But her description doesn't need to be the only one out there.
When you are with her, just try to be nice and have a good time with her. Bury the hatchet. Ask her to bury the hatchet too. After that treat her AT LEAST as well as you would treat a stranger. Say hello, goodbye, thank you, please, etc. Remember, at least as well as you would treat a stranger.
