We (me, my husband, my daughter) have been tested for both food allergies and food intolerances by our Naturopathic doctor using the Elisa/Alcat tests. One of the tests was a saliva test, the other one was a blood test. Neither were a big deal.
It is important to find which foods your daughter is allergic or intolerant to so that she can stay away from them. Over time if you don't find out what you're allergic or intolerant to, the body will continue to become allergic or intolerant to more and more foods because of Leaky Gut/Dysbiosis. In fact, the Leaky Gut needs to be repaired so that food particles don't continue getting into your daughter's bloodstream/body and further aggravating other body systems, making her fall prey to dis-ease and autoimmune diseases.
Also, if she does have Leaky Gut (and it's a sure bet that she does just because she already has food allergies/intolerances and has had them probably from little on?), she probably also has nutrient deficiences.
When I discovered my food allergies and intolerances, I was already 40 years old. I had a LOT of nutrient deficiences because of having had the food allergies/intolerances for so many years; my gut/intestines were VERY leaky. I am now on my 5th year of working on getting my intestines healed. If my parents would have known that I have a casein allergy (to cow milk) when I was little, I might never have developed my gluten and soy intolerances or the 21 other food intolerances that I have (as my gut heals, I am able to eat some of these foods every once in a while).
Once you have one issue with a food, if you don't take care of the issue/problem, you're just going to compound the problem by creating more food allergies/intolerances, which will then make your body weaker and make the body more nutrient deprived.
I would seriously urge you to take her to a naturopathic doctor to get tested for BOTH food allergies as well as food intolerances and to get her the correct nutriceuticals as well as supplements to help mend and heal her intestines so that her body no longer has malabsorption (which she most certainly has, just not a bad case yet).
Food intolerances can be just as bad and insidious as having a full-blown allergy, except that the symptoms take longer to be seen so it's hard to go back and find the trigger. If you get her tested for intolerances, the tests will tell you if her body has a hard time digesting/metabolising that particular food (or pollen or mold or whatever--the test tests for more things than just food, depending on what tests you pay for).
If you take her to a regular allpathic allergist, they do a skin test. We did do a skin test once (all three of us) to check for environmental allergies; if I had to do it all over again, though, I would pay to have the blood test through my naturopathic doctor. It's so much nicer, and you don't have to sit through all those skin pricks, nor do you have to worry about the itching that can come with putting something under the skin that you're allergic to.