Riding with Multiple Sclerosis or degenerative discs?

Hello,
I have a client that leases a saddleseat morgan from me, she has ms and has to take enfuron, riding helps her greatly and keeps her spirit up. The mare has the smoothest gaits, I love riding her myself,there was an older morgan on the give aways, I would hunt him up and give it a try,heck if I did not have so many, I would get him for myself.