About this one:

For reason 2, I could see if she just got reprimanded, a vitriolic email just isn't enough to let you know all the hate she has for you, so she needs to convey over the phone all her craziness. It's no fun to tear into someone if you can't hear their reaction. You haven't been responding to her provocations in her emails, so maybe calling you on the phone would provoke you.

If she had gotten reprimanded, she would have been more specific about mentioning it. Especially in a phone call, once the valve of the mouth is opened, its hard to hold back. And she wasn't holding back in the beginning of the convo.

She is feeling the pressure of the investigation. Some how, some way. She thinks that she is past the worst of it, however. But she realizes, deep down, she isn't. Her achilles heel is sticking out, and she knows it. She could have stated to the investigators that the D is well underway, and she needs SOMETHING to support that. You mailing here the waiver gives her that something. So that makes sense to me.

Send something nice to your MIL. Add some of the stuff from "ouch's" post, and make note of the wedding/gifts/sorry you can't be there.

Tell her you talked to WW on the phone. Tell her that she sounded angry in the beginning, but she had cooled off by the end, nothing more than that.