My moms heart horse had an injury that showed exactly the same as your mare. Im sorry, I havent seen the thread where you say what happened. Anyways, long story short Pebbs slipped backing out of a trailer(years before we had her), far as we know her hind legs went under the trailer and she did some serious damage to her hock. When we got her she had been sitting in a pasture for a year or two and had had zero treatment for her injury, someone basically threw hay to her everyday. She was a wreck, she could hardly walk. Her legs were very swollen. The vet said she had a bone spaven I believe and that the hock had fused, and that because of how it fused they would have to drill through the bone to give injections. Hand walking was her best friend. My mom would walk her everyday, at first it was literally a few feet and it eventually worked up to doing laps in the arena. We originally had her on bute, then Previcox, which literally saved her life. Her leg would "stick" just like your mares does in one of the videos. I had never seen it before in another horse till your video actually. Anyways, the vet eventually said to start riding her, despite the gimp as exercise was the best thing for her, and that it was less pain and more a permanent hitch in her giddy up haha. She would still look pretty off, and was just ridden lightly but it made a HUGE difference. What really helped was having a barefoot farrier who really knew what he was doing. It was a long process and we slowly weaned her off the Previcox and she is now only on MSM. Instead of doing the initial 2 dose loading scoop for the first week then half after she just always gets the 2 dose. Pebbles is now fully sound, although she'll always move a little different due to the fused hock. Her leg is permanently stocked up, and the hoof is actually a bit smaller than the others oddly enough. Her gimp is barely visible and her trot and canter are incredibly smooth. If injections were an option we would have pursued it, however her complete 360 has been amazing!
Live in peace,not in pieces