Do any of the states you'll be passing through require the use of seatbelts for passengers? Be a shame to get her all set up on the bed and then have to sit up uncomfortably for any of the trip.
Years back, my wife put her mom on the plane from Florida to Memphis. Went smoothly. If you request a wheelchair at both ends, you'll get express treatment, skip lines, etc.; and (at least in our limited air travel with my wife using a chair in the airport - bad hip), as her "attendant," I got to scurry along next to the wheelchair, skip the same lines, and so on.
And if any medical bobbles happen, there'll be trained staff at hand, not necessarily true on the road.
Neither way is perfect, and her opinion/desire matters a lot. As has been said, she might enjoy the sights better on the road more than in the air.