Sorry for the rather long response. I have a very strong possibility of being Celiac. Originally I went gluten free for another condition and was desperate to try anything to stop it. I (and others) noticed I started gaining weight (I've been underweight all my life) and my energy returned. After being gluten free for 2 years, I decided I wanted to be tested for Celiac. However, a person must be on gluten for an accurate test, and I was not on gluten, but got tested anyway. I had at least 2 strikes against me: (1) I have the genes (2) I have the blood line. My Dr. told me he had noticed the Irish tend to get it more, and I'm 3/4 Irish. Not to mention all of the GI symptoms that had gone undiagnosed since my teens.
This past spring I decided I wanted an accurate Celiac test, and with dr. approval, was told to go back on gluten for 2 weeks. After 1 1/2 days I lost all my energy and by day 3 the pain returned. So I decided it was not worth it and went back on gluten free. I consider myself Celiac, although I will never know for sure. But I have most/all of the signs. Gluten definitely bothers me.

I also discovered a few years ago that oats bother me, even those labeled gluten free.They are often processed on equipment that handles wheat items too (cross-contamination). My gluten free magazine ("Simply Gluten Free"), recommended I try Purity Protocol oats. They are organic (no pesticides) and grown in fields reserved only for oats and processed on equipment only for oats.
I've tried the enzymatic peptides that are supposed to help if you get accidentally glutened, but it did not work at all.

Gluten can hide in many places (soy sauce, soups, gravies, medicines, even candy). If your daughter is eating cross-contaminated foods (using shared equipment or shared cooking utensils), or eating hidden gluten, it could cause problems. Also there is something called FODMAP. I don't know what it is, but certain foods (like apples) contain items that can cause problems. I have been told by 2 doctors to eat my fruits and veggies cooked. They contain natural estrogen in varying degrees, and I cannot have estrogen. Cooking them kills the estrogen.

Thanks so much for your reply and all the resources you linked.

They ran an acylcarnitine profile and all was normal, so I'm not worried about the MCAD / MCT thing anymore, but her oral diet is still an issue. Wednesday she was served eggs twice as well as a grilled cheese sandwich. She then had yellow diarrhea and vomited twice the next day and threw up her NG tube both times. Since she's on an acid blocker, they have to x-ray to confirm NG tube placement; they decided not to re-insert the tube because of this. Aside form fat malabsorption being an issue, her arachidonic acid intake is incredibly high and I don't think Osmolite has DHA. I suspect excess prostaglandin (E2 or F2a) is involved in her nausea/vomiting; her symptoms are usually worse in the late luteal phase of her menstrual cycle - which she is now in. Monday and Tuesday last week were good days; she had been served what i would consider to be a healthful vegetarian diet - black beans, sweet potatoes, tofu (though rather high fiber for someone with intestinal damage). She did not vomit those days.

I finally consented to Remeron being added to her already long list of meds. I am scared, but I don't think there are any alternatives. You can't get medical marijuana in this state except for epilepsy, and even then, I don't think any hospital in the US can offer it.

I would love a 2nd opinion (and a different dietician!). I believe her Celiac diagnosis is correct and I'm certain that her eating disorder diagnosis is wrong. I suspect there may be some other factor that causes her Celiac symtoms to be atypical (though I understand that Celiac symptoms are highly variable). I don't know how to go about getting a second opinion, though.