Not exactly the same, but I have taken my mother on several short term trips in my TT (she is 80) and the biggest challenge is that she does things much slower than I do, so getting up and going is usually a bit of stress for me, but I try to not let it show. Now, I will say she and my dad were RVer's and I inherited the wanderlust from Her.
About two years before my dad died, I accompanied he and mom (along with their cat)in their small Class C on a 2 week trip. Daddy kept telling Mom, he wouldn't go unless I went. I did most of the planning, and all but about 50 miles of the driving. some of the things I did to make things easier: I showered in bath houses where we stayed. I tried to take some time with each of them separately, as well as a few walks by myself. Even though Daddy got sick, needed ambulance transport to hospital and spent three days in hospital, it was a successful trip. Daddy talked about it up until his death and constantly told me how much he appreciated me going.
One thing to make everyone feel better, is to write your location on chalkboard or whiteboard easy to see in RV. If you call 911, not having to try to remember address is going to make things go smoother. Also, if you stay any location long, you might do a quick search of local hospitals to know what is available. When we called for Daddy, the EMT's asked us which hospital we wanted to go to and we really didn't know what was available. One that was an option was one Mom remembered from her childhood (her grandmother had been in it years ago), so we chose strictly based on that. Turned out to be a good choice, but we really didn't have any idea.
So I say, if she is interested, GO and Take her.. make those special memories for your wife and your MIL.