So we had the vet out today. He had me trot her in a straight line, lunge her (she was an effing LUNATIC), palpated her back thoroughly, checked her legs and range of motion and had Shay-la ride her (she almost got bucked off).
His verdict? Psychological. She was a spazz on the lunge line, she was showing slight limping when ridden again, and blew up harder then she ever has on Shay-la, upon which she was pushed through it and actually calmed down. The vet does not think she shows any physical symptom which could account for blowing up THAT hard, especially when tacking up, mounting and being asked to walk elicits zero response from her.
ROFL, he's so funny, she was going absolutely loco on the lunge, roaring and bucking and leaping around, I had to run her into a wall at least half a dozen times to make her stop. He finally goes "In my medical opinion, she has a screw loose."
He advised for me to take it easy on her and see how she does after the move - cutting grain from her diet, and letting her have open space again. He advised lots of lunging to get her calmed down, more balanced and more muscled.
Also, she has sarcoids on her face. *sighs* I went to catch her today and she has a new one by her eye and one on her eyelid, along with the massive one on her cheek. The vet wants me to leave them alone for a bit and see if they go away on their own, and if not he has a cream he can prescribe that is apparently very painful and makes your horse hate you (hence why he's leery about prescribing it just yet if we don't have to).
She has one about an inch from the corner of her eye now to.
Well, at least we know now! Time to start getting tough with her.