1. There's a big puffy section of inflammation right in the sacrum area.
1.1 His chiro is on prenancy leave. For now I use this pad on him every day and it has reduced the swelling/inflammation lump by 45%. http://www.backontrackproducts.com/H...-Pad-p289.html I really wanted the sheet but it was too expensive and I needed something for this horse five minutes ago. This pad performs miracles, if you're dealing with old back issues; which I think you are.
2. She is always holding her tail out, or slightly up, and I saw her slightly flick it once. That is an indicator of pain somewhere up there. And, by now, as thin as she is, that pain may very well have caused ulcers; ask me how I know that:(
Second: "dressagekid4" may very well be onto something.
Hi there, I don't think this is a lameness. I think your farrier is on a good track. It looks to me as though her pelvis has been rotated (perhaps from a fall?) and is simply holding her in that position. This is not common, but it does happen and is very much a possibility. I would recommend Structural Integration or Rolfing sessions for her. They are not too hard to find for horses, and it works somewhat like a mixture of chiropractic/massage, with the horse's connective tissue. I have seen this issue fixed (literally, fixed) with this technique. I hope this helps you! Best regards, dressagekid4
Whether or not you've run out of chiro options within your driving distance, I really would take "dressagekid4's" advice and locate someone experienced in Strutural Integration or Rolfing. I'm betting they will at least be able to figure out what is wrong with her, somewhere up in the rump.
Even if you're riding her lightly, it's in her best interest to not ride her at all, until you can figure out precisely what is wrong. I wouldn't work her in the pen either - no lunging, backing, nothing. Let her do, at liberty, what she is comfortable doing