I was just posting about this earlier today. I think it would work, because the applications are installed separately and using separate folders. But Barbara would be the one to know for sure. Or, you/she could just try it and see - just back-up the images you are using now, just in case (game files too.) Tuna has used it that way, so if you have the same system I'm guessing you could too.

Hope your sis is doing well.