Stop leaving change in the room?

Seriously, there is no way to prove this is happening so you've done all you can. The manager most certainly took note, and if rooms cleaned by this housekeeper repeatedly generate complaints, then karma will run its course.

Also, I didn't know that individual property managers (at SHS particularly) had the power to grant higher levels of elite status. While I'm glad for you (and think you got a lot more than the loss of a few cents would seem to warrant), I have to wonder why Marriott would let their otherwise tightly-run program be diluted so easily.