goodness what a nightmare for you, i think that perhaps a second opinion might be good even for your piece of mind at least. hmm interesting he doesn;t think a pelvic problem could be involved with psd, perhaps a little shortsighted since if the horse is not working correctly then the line of strain placed on the leg changes and thus can predispose that area to injury, but hey what do i know i'm just an osteopath that spent 4 years at vet school!!! get a good osteop/physio or whatever and work with them with the farrier and the vet to get her right i'm sure there are lots that can be done to hep her mechanically and even if she has surgery it will all help the rehab anyway.