I don't know if I'll be much help...my daughter is the same age and has had the same problem. She has blown lunch while walking with me across a parking lot...very weird. She doesn't have low blood pressure or the other problems. It must be very difficult for you. My daughter tried a medicine that helped cause the food in her stomach to pass more quickly to the small intestine. In other words her stomach would empty faster (in the right direction) and there would be nothing there to come up. That helped a bit. The thing that worked best was omerprezole (prilosec) 40mg (usual dose is 20mg). I needed special permision form the insurance company and then they paid for it so I wouldn't have to buy it over the counter.
She has actually outgrown it a bit, but now she started high school and is in honors classes and sports so she's a bit stressed so now I have her on 20mg preventative. We'll see if that holds her.
Good luck with your daughter.
you can only suck at life if you let life suck at you