Lake-
In the days before "adaptive" and all the programs existed, one of the guys in our dive club had only one arm. And he was certified just the same as anyone else, and could out-dive at least 3/4 of the other divers with no problem. Yes, he had some "special moves" in terms of being able to sling his mask back on and such, but having limited use of one arm shouldn't stop your wife from diving at all.
Ask around, find a shop with some instructors that are willing to work a little harder and perhaps are already familiar with the problem, and if anyone says it is a problem for them...move on down the list. If there's no one local, turn this into an opportunity to take a vacation and let a better shop in a nicer place get her certified while you're doing something else.
Plenty of folks have two good arms, and STILL have problems hoisting, carrying, or setting up their gear. The trick is all in just planning, and outsmarting the heavy stuff.