How much is too much?

I'd sit down and be the bigger person. If she loses it or stops going off, say very calmly "_____, you're acting like a child. I am trying to be an adult and you are not working with me here. This anger you have hurts <b>you</b>. If you want to talk this over and work it out, and let go of all this animosity that you harbor toward me, please let me know."

Nothing will piss her off more than you being calm. So you <b>have</b> to stay calm.

She'll get irritated at herself that she can't upset you or break your calm, and hopefully one day she <b>will</b> realize that it's only hurting her. And hopefully you'll hear from her shortly thereafter.

Hang out with your brother, but let him know that his wife is out of line - and that it's hurting her. Get him on your side. Keep hanging out with him and realize that she is not important to the relationship you have with your brother. <b>And be calm!</b>

Don't worry about her - she doesn't matter, in the scheme of things. Be nice to her, even if she's shitty with you. Also, <b>be calm</b>.