Geez, I'd be SO tempted to comment on her Facebook status "exciting, I know!
" as if it was mean as a happy status.
I think, well I hope, you just caught her at one of those overwhelmed times. Like maybe that day had been: boss gives her a hassle about something that is not her fault, FMIL announces she's taking over the DJ selection on and BTW its a guy who specializes in Polka, 4 RSVP cards came in the mail with added extra guests and the catering bill came in. And then she heard about the house stuff and flipped. Hey its possible, right?
So I say let things settle for a bit and let yourself also calm down a bit, and then address it. The reality is most people who get married have at least one of two if not both of them move right around the time of the wedding. Its actually pretty standard, she's not going to get too much sympathy. And most people have to pay a heck of a lot more then just utilities for their homes, so again, she's not going to get a lot of sympathy. And you are giving her 6 months notice - I've known people who've gotten 6 weeks notice their landlord was selling the house. Her eyes will open.