MOTHER IN LAW HAS LEFT THE BUILDING!!!
She was actually on really good behavior all week. The main thing of note was when she somehow got her hands on some mushrooms (from where, I have no idea). She and FIL apparently ate them before my husband and I took them out to a fancy "goodbye" dinner last night. We didn't figure it out until they started giggling uncontrollably at the waitress. Yes, these are grown adults. No, they did not offer to share.
Tonight I'm ordering greasy Chinese food (thanks, sugarhill!), cracking open some wine, and renting a movie that we'll watch in blessed, blessed silence in our much emptier house. Bliss.