We all ramble. It is difficult to help when one has never seen the horse, but I find Mare Magic worked wonders for my mare, and Smartpak Muscle Mass gave my gelding a topline (went from looking like a scrawny pony to pinning in conformation classes) and helped him to be a lot more flexible. It might be a good idea to call Smartpak and discuss options rather than relying on the Forum.
When I suggested bareback, I meant for your legs to just be like limp pasta. You should be able to stay on just by balance, without using your legs at all. You longe her in a bit? Try using a cavesson instead, with side reins, longe surcingle and crupper. Different methods work for different horses, and trial and error is sometimes the only way to figure out what best suits your horse.
Thoroughbreds are no hotter than any other breed – nor are Arabians. That would be a myth.
It is never the horse's fault