Much of the advice already given is great….it definitely sounds like you need to support the yearly hock injection by providing a constant joint feed through. The best ingredients are Glucosamine HCL at least 10,000 mg, msm at least 10,000 mg, chondroitin at least 2000 mg, Hylauronic Acid at least 100 mg, Hydrolyzed collagen is a bonus. I’ve listed high amounts for these ingredients because you already know she has arthritis. Many (most) support products have less amounts (for these ingredients I listed) for preventative maintenance and will not give you enough positive results. Also consider she may need twice a year hock injections although personally I would opt for a general injection of Pentosan (most affordable), Adequan or Legend on a monthly basis (after the initial loading dose). Then consider affording help for the hindgut..I know this sounds unrelated but I have very consistently found that horses getting sore are also holding themselves because of hindgut inflammation (caused by a multitude of possible reasons, work being one of them). I always put all my horses on smartpaks ultra digest. I occasionally give Devils claw after a more strenuous workout. I know your sport is different from mine, but consider building some different strength through dressage eork to support her abilities better. I’m a 25 yr experienced dressage trainer; through use of training techniques, feed throughs, and in a few of my own horses, of in general injections, my “kids” stay sound even though they get trained to the highest levels. There’s tons of info on the Internet to put together a solution for your own particular situation!