She should definitely get a full understanding of what the housekeeper position entails, in exchange for the room and board. They might expect her to be on duty more hours than is reasonable or something like that. I know she was a sub to him, and so she probably wouldn't mind that too much, but when your living space hinges upon that sort of thing, I would be very cautious. You would have to be certain that it is treated as a real, professional agreement without personal issues/expectations getting in the way and potentially putting her in the position of having to move out if bad feelings arise. I think it could get sticky.
I agree that it sounds like a better situation if you and she move in together, closer to Ginger. Maybe you can find a place big enough to each have your own private spaces.