Did your child have a fall when she was 6 years old, before the migraine's started? (maybe not even a really bad fall, but a twist?) Like PTree said, she might need someone to check out her back/spine area for an adjustment. Keeping a diary of the food she eats and the times she gets them is a great idea! I looked up 8pm on the Traditional Chinese Medicine organ/time chart and 8pm was the peak time for the Pericardium to function. The Pericardium protects the Heart. Don't know what that means in her case, but just thought I'd throw it out there to add to the mix. I hope you can figure this out...migraines are just awful, poor little girl.
PTree, do you not think that even 1 b&p drink a day (1 tsp of b mixed with 1 tsp of p) might help her get some of the toxins out of her? For only a limited amount of time...say for 2 weeks? Hmmmm...