What Is Causing Voimitings In An Infant After Taking Food?

My 6 month old started vomiting all of her food a couple weeks ago. We had started some solid foods and had been doing rice cereal with milk a couple weeks prior to that. She started to lose weight, and had started to get dehydrated. Our pediatrician assumed GERD was the cause at first so prescribed some Axid. Things got worse. We ended up taking her to a after hours urgent care for kids. She is now in the hospital and has been there almost a week. Has had many tests done. They can t get her to keep down the contrast when trying to do an upper GI. She is now on a feeding tube with breast milk at 30mL an hour. She has been keeping a lot of it down, but after being on it almost 12 hours last night and 6 hours today she has had some vomit again and they stopped feeding her now. We are waiting on further orders from doctors and are growing increasingly concerned. What questions should I be asking the GI specialist? And what key things might I be missing to helping the doctors diagnose her?