She's proven she's incapable of acting like this with my husband. There's just too much deep-seeded (fill in the blank... resentment, anger, jealousy, etc.) It's all too emotional, or whatever, and she just blows up at him. He and I could say the same thing to her, but coming from him, she'll blow up. Not saying YOU'RE the emotional one in your case, it's the same if he's the emotional one too.
Perhaps, your ex's wife is just trying to help. I know it may seem controlling (and maybe it is) but like me, maybe she thinks she can help with the situation since there's a lot less emotion between the 2 of you than between your ex and you. Just a thought... but I would definately go. And like sy mentioned, just go with an open mind and hear what she has to say. It may do a lot of good.