You could be dealing with pain, neurological deficit, or muscle disorder. Without the vet exam, it's all just a guess especially from people who can't see the horse. I would not ride this horse and would put her on small paddock turnout. Stalling is a bad idea with some issues so err on the side of caution, don't let her have room enough to run and act crazy but don't make her stand in one place all day either.
I would definitely go with the time and expense of seeing the equine vet because there are just too many things that can be wrong and a small animal vet is not going to be as up on current issues in horse medicine.