This sounds like nerve pain. She probably has a pinched nerve in her back. This would account for the 'sudden' pain. She would react like she does with that kind of pain. She also would be scared, because she doesn't know when it will come back. I would ask for a specialist; either an orthopedic doctor, or someone that knows the spine well. I would also ask for a copy of the x-ray that showed the bone spur.