I would see what the Vitamin D does, then if she is not feeling better, take her to a chiropractor. Maybe the Internal meds Dr. is missing a pinched nerve or curved spine. you didn't mention if she has had an x-ray of the area.
It is very scary when a child is sick for so long with no explanation. I would, if I was able to, see some specialists. Who is in control of her health? Is that doctor seeking a second opinion? If not, and you don't think it is in her head, I would follow your intuition and get some one else who will dig deeper. On the other hand, if it were depression, why would the doctor not suggest she speak with someone instead of brushing it away?
I had a friend who took vitiamn D pills and she got so sick from taking them I would talk to the dr again to see if that what could be causing the problem eat vitiamn d enriched foods get her out in the sun
Welcome to the MedHelp forum!
In your daughter’s case was disbetes, hypothyroidism, Hashimoto’s thyroiditis, hypoparathyroidism, polycystic ovary, hormonal imbalance, adrenal gland problems etc were ruled out? I suggest you consult a good endocrine specialist. Also stool should be tested for worms. Hope this helps. Take care!