Something to consider is the relative size between hubby and wifey.
I am 5'1 and hubby is 6'2. I am comfortable driving our small class C, towing or not but I don't feel safe driving the bus. Reason is my size: I can't see over the instrument panel in the bus. The seat is air ride but by the time I get it adjusted to be able to reach the pedals, you could hide a Suburban or two in my front blind spot. ;)
During my military career, I drove all manner of motor vehicles, some quite challenging. I'm sure if something happened to the hubby I could grit my teeth and get us home, but why put hubby through the stress if not necessary?
My point is, ask your wife why she doesn't want to drive, she may have a similar reason.