I am so sorry your baby has to go through this. It is a horrible feeling to watch your child hurt. Has anyone considered migraines for your child? Kids DO have them. I had them at 4, my oldest son at 2 and my other two kids at 6 yrs. If she is on pain meds you probably should not stop them all at once, even if it has only been a week or two. Kids are more sensitive than adults.
Ask the doc if you can try a triptan med to treat the headache. Triptans are Imitrex, zomig, relpax etc.. If they work your dau has migraines. Even in kids migraines are treatable. There ARE meds to prevent migraines, some are very well known and have been used by MY kids. Ask your doc, and get a neurologist (pediatric) to consult.
take her to a doctor to have checked out. RMT's can help with some kinds of headaches too. see what the doctor refers you too.