In your place, I really would make an appointment with a neurologist asap for a basic clinical exam, see what they say, and then go from there. I would not dismiss anything as a quirk. Especially as your vet has already suggested the problem may well be neurological. If she does have SM, you have the broadest range of choices when it is caught early. Sm typically will affect one side more than another. You are seeing a lot of correlation to the same side which to me would be flagging a serious need to have a neurologist check this out. If it isn't SM, to me this still sounds neurological.