Well, I can relate. Sigh. My eg/pg DS7 was like your daughter before starting neurofeedback and a diet six months ago. He was born with severe sensory issues, including with food (i.e. textures, tastes, etc.); he had feeding delays, spent two months in an outpatient feeding hospital program, and had years of feeding therapy. DS is tiny too - 5%. He's still in 4T.

DS just finished 6 months of neurofeedback yesterday, but we're planning to continue with the diet (no dairy, no gluten, no artificial sugars/dyes/etc., limits with fruits, etc. - similar to Paleo and Feingold diets) because it's been so beneficial. Basically, any food that converted to alcohol was either eliminated or greatly reduced, which seems perhaps drastic and overwhelming until you realize that there are lots of alternative food products today.

After going through years of feeding issues, there's definitely a behavioral component with eating. However, I really do believe that there's also a neurological component, which is too often ignored.

Sugar is on the tip of the tongue and I do believe it was neurologically affecting him, somewhat similar to an opiate. See http://www.radiantrecovery.com/. This is one of the reasons why they give patients at the outpatient feeding hospital program Oreo cookies - they just want them to eat (they're not concerned with nutrition; they're solely concerned with the behaviors associated with eating).

What I did notice from switching to the neurofeedback diet is that once your body gets used to having the proper nutrients it needs, it doesn't usually crave the other stuff. It also helps, though, if the candy and junk food are out of your sight, which is easier to remove at home like you said but less easy to do outside the home. I try to counter this by finding alternative recipes, such as black bean brownies, and making them available at home, even for breakfast.

You could see a nutritionist or dietician. Or read some books or websites. Or you could try experimenting with a diet log yourself and see what works/doesn't.

I wish I had something more concrete to say, but the food stuff can be a long haul - especially if you've got a sensitive child.