Could it possibly be a Chiari malformation? I wouldn't have normally thought of a CM with a dog, but I just admitted a (human) patient with that dx today, and she has numerous neurological problems, including blindness. Basically it's caused by the lower part of the brain protruding down into spinal cord territory, where it shouldn't be, of course. Treatments include steroids & surgery, depending upon the symptoms.
I'm glad Jane did well with the MRI, and am keeping her (and you) in my prayers.