There are a ton of issues which can cause failure to thrive in infants. I think you are doing an excellent job finding a new GI and working so hard to offer her solids before the Pediasure. There are some pretty strange allergies out there, aside from the eleven you hear about all the time, and its hard to diagnose allergies in infants (Corn, Oats, molds...etc.) . If you are waiting on test results for the EEG and an MRI my course of action would be the following; keep up the pediasure and offering solids, and pretend you are a nurse. Keep a chart/ notebook of her intake and her temperature three times a day. If blood sugar is an issue, start taking that as well. Sending you hugs and support.