How old is your dog? I would take her to a specialty clinic or university clinic that would have both a neurologist and an orthopedist. My 1 year old deaf rescue girl who is a herding/spitz mix has shuffling feet, tremors, and other problems. She was seen first by the neurologist and they suggested x-rays and more testing. My regular vet did take x-rays of the neck, back and hips. I took her to an orthopedist to review the x-rays. Since she was a stray they do not know what caused the problem but it was suggested distemper or perhaps another infectious disease. I just took her to an opthalmologist and her eyes are good but she does have sensitivity to light. Distemper almost always causes eye problems. The specialists are suggesting an MRI of the back, neck and a spinal tap for her.
If your dog was adopted as a puppy or an older pup, I would check with the Humane Society to see if she may have had distemper or some other disease.
Did she have an accident where she might have injured her back or neck?
You might want to look into getting a doggy wheelchair since she has good movement in her front legs.
I am sorry for the problems your girl is having and I hope you find out what is causing it.
Jennifer