Hi S.,
I survived reflux, colic and 13 solid months of daily puking! Nothing more than Mylecon went in him for help.
However, a couple of things in your email caught me. Stop letting her eat and then putting her in the car. Feed her where she can digest without a car ride following. That would be elimination #1. Then, if that works, most of the problem is solved. Then work on the 'cut up sizes' of foods.
My second thoughts after reading through your post....I assume the dr prescribed the meds for the reflux? If not, please check with him/her. My thought on this is a food allergy....Celiac is a common culprit in many things. If she is eating breads, breaded products (like chicken nuggets) pastas, wheat/flours, etc., that could be a culprit in this whole event as well.
My kids don't have Celiac's but I have several friends whose children do. One is my god daughter and what a difference it has made in her to be off gluten and on other foods. It is relatively easy these days due to so many 'knowing' they have it and the regular grocery stores carry products to help- otherwise it's the health food stores.
Start with #1, make sure the dr is involved, ask about Celiac or it's possibility. Good luck and check back with us for an update.