I would be going to a different Vet post haste. There could be an injury in her spine, that's what we had. Dragging toenails like that is a symptom of more than one thing. Dogs are pretty stoic but your girl could be in considerable pain.
What exactly did the Vet do? No X-ray? Drawer test? No pain meds? No protocol to follow? To mention only the few I can think of. Are you sure you actually saw a real Vet?