I would make an appointment with a pediatric neurologist for a second opinion.
Did she suffer an injury prior to developing these symptoms? (It doesn't have to be a particularly dramatic accident.) One of my daughters had somewhat similar problems (but more serious, she was a semi-invalid) and after four years even the best pediatric specialists could not diagnose her problem. I had mentioned she was in a car crash and then banged her head once after that. But my information was shrugged off.
We had been out of the country for a great many years and so I was not aware of the increasing interest in alternative medicine. But someone suggested I take her to a very well-known chiropractor. I did. He confirmed that her spine and neck were out of alignment, very possibly the result of an accident, and that her symptoms were consistent with compressed nerves. It took two and a half weeks for her to be pain free and smiling, That was in April. By summer she was riding a bicycle. I am not a particular fan of chiropracty per se, since some practitioners seem to be ham-fisted. We lucked out on our choice. He was slow and cautious and gave very helpful advice. He does not subject children to x-rays as he feels it affects their growth.