Hand sanitizer is a decent idea and it only takes a second to put on. You can just get the alcohol-based stuff and not the anti-bacterial stuff which many people (including me) don't care for. It is a bit drying on the hands but other than that I don't think it is harmful.
Also, would she dig a foam pump soap thing? I am 28 and I think they are so cool

My mom has one that I use all the time when I visit...
Maybe you could cut a deal where washing after peeing is optional (still preferred, but urine is sterile)... but that there needs to be some form of hand cleaning after poop because that can honestly make you or someone else sick....
Good luck!
ETA: we posted the same suggestions at the same time...whoops!