Yes, if a horse is crippled and arthritic lets just throw bouncy children on there and walk them around. This is why I hate the pony party business. People see in green vs the welfare of the horse. I had a neighbor who put 50lb kids on a freaking miniature for christsakes. Didn't care if their feet were too long, didn't care about saddle fit. Unbalanced riders are uncomfortable whichever way you put them. Her sound horses were tired of hauling kids around after an hour. You should just euth her and save her from that fate. Or give her to someone willing to work out her problems. If you lived nearby, I'd take the poor thing at this rate just because you mentioned pony parties; and get her... Iunno, a chiropractor? A massage therapist? It's amazing what they can do. There was a horse that was lame for like, a year that the owner donated to a rescue; after some chiropractic work she was sound again!