So DH took MIL out to a local pub for dinner last night - the premise being that it was "neutral ground".
He explained that he was deeply upset by her behaviour towards me and in general. He explained that I was working and shouldn't be disturbed unless in an emergency. He went at great lengths to define emergency to her. He told her that if her behaviour continued, we would move. He told her that she was welcome to prearrange meet ups with her, but she was no longer welcome to pop around at her convenience. Her key would not be returned to her. (Unbeknownst to her, FIL now has a key, which he keeps in his wallet). DH also told her that if she ever insulted me again, we would move - he said that it was unacceptable to speak to or about anyone like that, least of all his wife. He told her how incredibly angry and disappointed that made him feel and he couldn't imagine how I had felt.
He said he loved her, and enjoyed spending time with her like on Saturday, where there was no drama.
She interrupted him a LOT apparently, and cried. At one point she got hysterical so DH simply stood up, and turned to leave and she immediately calmed down. He said that if she caused drama, he would simply leave. That seemed to get her to listen better.
They got back about 9ish last night and, after asking DH, MIL actually came to the door and apologised for calling me a bitch. She said it "all got a bit much" and that shed been "very wound up" so Im not sure she fully took responsibility but still.
Hopefully she won't disturb me today, DH has given me strict instructions to ignore her if she does.
DH has a very quiet yet forceful manner, tbh I'd have probably cried if he had told me I'd disappointed him.
Let's see how it goes.
I hope I've explained it properly.