Really, the best way to identify food allergies is a challenge diet. Skin tests and blood IgG/IgE levels aren't as accurate, for one thing, and plus when you're doing it yourself, you can test for allergens that your allergist may not have antigens for. It's a PITA... but then, sticking to an allergy diet is a huge PITA too, so she may as well get used to it Myself, I'm lucky that I don't have anything horribly severe, so I just manage my allergies, and I'm only really strict about my diet when the pollen counts are through the roof.

To do a challenge diet, you have to begin by eliminating all allergens from the diet for at least four days. Then re-introduce them one by one, a day at a time, and see if you have a reaction. Which, a reaction to a food usually doesn't show up immediately unless you're very sensitive, it's often a matter of how you feel several hours later, or when you wake up the day after you eat it. So keep a symptom journal and a diet journal.

If you're going to eat anything you don't prepare yourself during the challenge (or afterward, once you've identified a trigger), get a *complete* ingredient list, and be aware that things like corn oil (for example) contains trace amounts of corn proteins, so those have to be eliminated to get accurate results from the challenge. Yeasts/molds are especially hard, because it means no vinegar, no mushrooms, no sauerkraut, no alcoholic beverages (even distilled ones - trace amounts, again), no pre-prepared fruit products like juices or jams, and no fresh fruit that can't be peeled. "Aged cheese" means anything other than pressed or pureed fresh curds - i.e., cottage cheese, mascarpone, cream cheese, ricotta, paneer, but nothing with cheese culture, which is a mold again. Miso, tempeh and soy sauce are cultured with molds, too, as well as more esoteric Asian products like natto and preserved tofu.

Once she's identified her triggers and/or allergens (if any), she may or may not find that, like me, she can have small amounts without making herself horribly uncomfortable or triggering a migraine. But to do the challenge, you have to be really strict.