I just don't see this being a neurological problem. I think a vet can make any horse look lame if they cross enough legs and spin them around enough. I had a vet tell me my horse had EPM 4 years ago. I was brand new to horse ownership and took his word for it. Looking back I think he was completely full of it, and it was a simple lameness issue. Your horse does look stiff in places, but if he had something as severe as EPM, she would have been falling over while trying to cross her legs.
If this were my horse, I'd give her some time off, ease off on the bute if you can since it can really aggravate the stomach. Add a ton of vitamin E to her diet to assist her body in healing itself and stop looking for a worse diagnosis. I know it's hard to not worry about your own horse, but she just looks stiff and sore.
The only combo diagnosis I can think of would be a tick borne illness which can affect the joints, cause soreness and present as a neurological thing. Lyme disease can ebb and flo and flare up from time to time if it was not treated at the time of the first infection. There's a few vet students on this forum, so hopefully they will weigh in.
You just have to see your distance...you don't have to like it.