She's done it again

You know who I mean. Yes, my MIL from hell.
Her holiday plans this year were devised (so I believe in my paranoid little corner of the world) solely to bug me shitless.
We specifically told her not to come in the first two weeks of September because it wouldn't be convenient for us. So when did she arrive? Yup, 5 September. And no, it wasn't convenient because my dad was here. But we survived.
Then there's the fact that no return-to-Paris date was mentioned. Then she casually dropped it into the conversation that her friend (a nice lady she spent the first two weeks with) was going back to Paris on the 19th (yesterday) but that she "hadn't decided what she'd be doing next". Grrrr.
She then spent last night with a friend who - of course - just happens to live here in Montpellier, and she said she'd stay there till Tuesday, before going to Barcelona to see family. Her plan was then to come back here next Friday, spend 3 nights (because of course we said she could spend NO MORE than 2 with us) with us and head back up to Paris on Monday afternoon (28.09).
Then she phoned back an hour later to say that in fact she's too tired (from what? She's done nothing for 2 weeks...) to go to Barcelona and will now be arriving here, with us, TOMORROW night.
The only plus points to this that I can see are that a) the ordeal will be over quicker as a result and b) she'll only be here till Wednesday, which is actually only 2 nights.
On the down side are the fact that the girls will be in bed too late with her here, I'm not prepared and have had to wash yet more sheets, I'll have to make and remake beds all week again and tomorrow just isn't convenient for me as I'm teaching and have a PTA meeting in the afternoon, followed by the PTA general assembly all evening.
I swear, this woman is enough to drive anyone to drink.
I'm hoping, of course, that we have a major argument (yes, I'm evil) so that we can be rid of her for a few months.
Grrrrrrrrr