My little vote is that it is time to call the vet for a chat and a work up before throwing product after product at this. Being from the land of Lyme, these are classic signs, but they could also be indicative of something else entirely. A Lyme test may be in order. I would call the vet.
I am usually one to suggest ulcers, but I do not think that is the main problem here, although it may be contributing to some symptoms.
I would honestly think about going to a very good lameness vet. Given that it could be anything from spine, joints, soft tissue, or a neurologic issue, I think that would fit you best to try to figure out what is going on.
I don’t know how much money you have to spend on this mare, but realize it may very well take several visits to figure this out, so you need to be prepared to stick with the vet even if there is no improvement. You need to give them time to piece together their findings, rather than switch to someone new. A good lameness exam and perhaps a bone scan would be ideal. I think the spine or SI could be the culprit, but some of your descriptions make it sound neurologic. Really what you need is a vet with a good eye and lots of experience with musculoskeletal and neurologic issues to watch the horse go and do diagnostics.
What Eventer13 said! Sometimes it takes a long time to piece things together to make an accurate diagnosis. 
I would second or third the suggestions to stick with one vet rather than repeatedly switching, and start from square one with that person and go slowly forward ruling out specific possible causes, rather than just guessing.
There’s a great quotation from one of our FEI/USEF vets, I believe, and I’m sure someone here can cite it more accurately than I: “Absent a correct diagnosis, all medicine is poison, surgery is trauma, and alternative remedies are witchcraft.” (emphasis mine)
Slow down, find one vet/chiro/farrier team to stick with, and be patient. Good luck!
[QUOTE=Calamber;7583628]
Oh, missed that Gumshoe. Also no point in scoping, just treat, and just as an fyi, hindgut ulcers do not scope.[/QUOTE]
Ditto that!
I love magrestore…it has been great for my horses
OP, you described exactly what my 17 yo appendix mare was doing. She went from a kid’s horse to unsafe in a month. After two vets, blood work, scopes, etc, all negative, I was told that it was probably behavioral. I had read on this board that hind gut ulcers were not able to be detected so I treated her for that. Assure Plus and Assure Guard for a month and then Assure Guard every day fixed the problem. It took about 45 days. Maybe something else was the problem and it healed in the meantime but I am keeping her on Assure Guard anyway.
