The only experience we've had with a 'C' is renting one. We found the front is narrow but the rear wider which is a jolt when trying to park. I guess with more time we would have felt comfortable with it but we really had a hard time judging distance side to side. Also, with an 'A' you are sitting up higher and can see upcoming traffic issues much better. Holding tank size might be a problem depending how you use it.
I wouldn't advise jumping down to a 'B' from an 'A' unless you just drive from place to place like you would a car. They are very confining - to us, anyway.
As stated above, give her private RV driving lessons with what you have first before changing.
You're correct that both people should be able to drive and do the hookups. We've made good use of that philosophy a few times with medical issues.
We have friends an he had a moderate stroke. They both wanted to continue RVing because they really enjoy it. She knew how to drive before the stroke and now she is the sole driver. Their travel habits haven't changed. If you were a single RVer a situation like that would just necessitate you quitting immediately. As it is, they still have the enjoyment of traveling.
Good luck!