--what trips off an autoimmune condition like celiac; environmental "triggers" are certainly suspected, but not proven beyond a shadow of a doubt. The main theory involves molecular mimicry--some pathogen invades the body, the body mounts an immune response, even fights off the pathogen, but if the pathogen has a molecular shape that is similar to some body tissue, the now activated immune system cannot distinguish friend from foe and goes after body tissues with the same molecular configuration. It is thought that some of the gluten peptides have similar shapes to villious tissue, AND also similar shapes to certain proteins that make up tissues in the peripheral nervous system and in the brain's cerebellum--this is why celiac and gluten sensitivity can present with neurological issues as well as gastrointestinal ones. And, of course, if the gut is affected and nutritional status is compromised, all sorts of symptoms may occur, and these may be vague and hard to put together.
Celiac/gluten sensitivity is not quite the same as wheat allergy. The latter reactivity is relatively fast, mediated by IgE antibodies. The former tends to be slower, and mediated by IgA class antibodies--but it can lead to more thorough damage of tissue.
By the way, there's no reason for daughter not to be using oral B12 supplements--shown to be as effective as injections and often longer-lasting and more able to keep stable B12 levels, with no known toxicity level; the Snow medical textbooks and Family Practice Notebooks discuss this and links to these can be found in Mrs. D's B12 thread in the Useful Websites section of our neuropathy forum:
You definitely need to be looking through Cara's (alias JCC) The Gluten File, which can be linked to at the top of this forum--as far as I'm concerned this is the single best database in existence on all things gluten, with links to tens of thousands of papers and monographs, all nicely organized. And I know Cara would be interested--her search into this started with vague feelings and B12 deficiency, many years ago.