I would agree with the Pediatric Neurology consultation. If you are in the area, we have a pediatric neurologist, Dr. A. David Rothner, who specializes in pediatric headache. There is a form of migraine which results in repeptitive vomiting/nausea, which can be treated. If this is not the cause then other conditions such as
autonomicAutonomic nerves
Autonomic neuropathy dysfunction (given her BP change) or gastro-intestinal disorders should be evaluated. I would recommnend seeing specialists at a academic center, such as ours, who have all of the physicians available. Good luck.