I hope it is some kind of toxicity that you'll be able to treat & failing any other answers, I'd consider changing her feed & speaking to your vet about how you might 'detox'. Australian 'stringhalt' - as opposed to this condition in other places - is one thing that comes to mind with those kind of symptoms(& often 'high stepping' hind feet, inability to back up). It is (thought to be)caused from eating a lot of flatweed and can(not always but often) be treated by removing the cause immediately & mineral therapy to correct the imbalances(without looking it up, I think suppression of Mg was the biggie). A friend of mine also had 2 horses with sudden, inexplicable symptoms like you describe. It was deemed some kind of fungus or mould in the hay was the cause & they were treated, I don't know what with I'm afraid, but one of them survived & became fine again after a while.
Only have 1st hand experience of one confirmed 'wobbler' and the vet deemed it was from being 'taught' to tie up too early & roughly, that it caused damage to the spinal cord when the horse pulled back. The horse was put down shortly after, when he was 2yo.
A horse I found(it had been found in the bush, ranger called me...) was in a lather of sweat, rather exhausted but apparently OK, but intermittently she suddenly was far from OK & acted 'drunk', especially in the hind end. Owner came to collect her & said she started acting funny 2 days earlier, escaped the night before by jumping out & they'd searched for her all night. Horse collapsed at the door of their float, dead! Autopsy(rich owners!) showed a brain aneurism, cause unknown, but suspected trauma to the head.