Sorry you're having to deal with this.
I suggest beginning a food log immediately. It will be of great help to the gastroenterologist.
The easiest way to do it is to buy a simple notebook or legal pad. Use one page per day. Write down the food she eats during the day, and be specific. Don't write "snack", write "1 Granny Smith apple and a handful of Teddy Grahams", for example. You don't need to measure things (you don't need to write that she ate 3 ounces of something, just an estimate of the amount), just jot down what she's eating and drinking. Again, be specific with the drinks. Drinks can be confusing. For example, a carton of kiwi strawberry juice will often have apple juice as it's first ingredient. Try to note the time of her meals and snacks and beverages.
When she mentions abdominal pain, and/or vomits, note that in the journal, and make sure that you make note of the time of the episode. I know it's unpleasant, but you should also note what she vomits: liquids, undigested food, mucus, etc. (My daughter has gastrointestinal diagnoses so I've done this a million times.)
I have kept logs of all kinds for my daughter. I put a post-it flag on the pages where my daughter has experienced whatever it is I'm keeping track of (sleep issues, vomiting, panic attacks, etc). That way you can point the doctor directly to the episodes.
You might notice a pattern, or the doctor may, but a journal will be a really useful tool.
And try not to consult with "Dr Google" prior to seeing an actual doctor. It's one thing to look up symptoms if you don't know where to start, but you're being referred to a specialist, so just focus on the food journal and try to stop worrying. She may be sensing your anxiety and that might be making things worse.