I don’t know if I missed it or not, but has anybody done a lameness exam – you know, flexion tests. Those aren’t too expensive and will at least indicate whether she even needs injections. My then-15 year old gelding had very bad hocks – would buck if you asked him to canter and couldn’t walk straight down a hill. He had steroid joint injections, which only improved function for about the length of recovery time (4 weeks). The vet then recommended ethanol joint injections, which I thought about long and hard and finally had them done. These injections accelerate fusion of the bones in the hock and kill nerve endings in the hock so the horse doesn’t feel pain while the joints are fusing. He now gets Cosequin 2x a day and an Adequan injection every month. That and access to regular exercise keeps him feeling good. But first do flexion tests to see if your mare really needs anything major done.