I was going to suggest the same thing as toolman - send her an email back saying that you're sorry for her feelings, but that she needs to do X, Y, Z to fix things and to expect less time with your family until she does.

If your husband won't take a more assertive approach, then at least get him to commit to something like "if your mom does something like X, then I am going to tell you that we're leaving and you need to support me in that and just leave. If you want to argue about it, we do it when we're home and no one else is around."

I like the toilet paper idea, haha. If she was to ask why the toilet paper, you just have to go "Well, you talk a lot of sh** so you may as well put it where it belongs..."