limited ingredient diet from early age?

[Willow and J]

This may have go to the food group or to the AD group, but I'm not really seeking an answer, so I decided to put this on the general discussion.

Willow has Atopic Dermatitis, and she has been on limited ingredient diet for almost 2 months now. She eats kibbles made of kangaroo and lentils, and we asked a friend of mine to use only things that are in the kibbles and make dog treats for Willow (so lucky to have a friend who can do that for us!).

We see quite a bit of difference! She's scratching less, even though this is the time of the year that we'd see her getting worse, and we have decreased dosage for claritin. Willow will also be in for allergy test and possibly immunotherapy in three weeks, and we're hoping that combining these two will tackle food, seasonal and indoor allergy that we suspect she has.

We've fed her grainfree kibbles from very early on, around 6 months, and before that, she was on "good" food (Wellness, Artemis). We also switched kibbles to different formula every 6 months or so, so that she got different kinds of meat in her diet. One of the difficulties that we faced as we started suspecting AD and started thinking of limited ingredient diet about a year ago, she already has been exposed so many different things and we were left with very little choice (only two, either rabbit or kangaroo). Also, some of the kibbles that we like the best such as Orijen (Willow's coat became so shiny and beautiful, and her digestive system was very happy when she was on Orijen) includes so many different ingredients (including fish that Willow didn't do well on from early on - her ears, nose, and feet flare up and gets very itchy) that we sadly had to stop it. 

Thinking of all these and given how she's much better on limited-ingredient diet, and also thinking ahead for a possibility that Willow might develop an allergy to kangaroo (then we'd do rabbit, but then, what after that?), it feels like that we would have had more options if we put her on one meat at a time from very early on. But, having said this, I feel that there's some fault of logic here, or maybe I am not understanding food allergy very well? Puppy formula is made of various protein no matter which brand it is (and of course it makes sense because puppy needs various nutrients), so by the time a dog is diagnosed with AD, usually around 1.5-2 years, the dog has already been exposed to various different kinds of protein/meat.

So, what if we fed Willow much simpler diet from very early on, one protein at a time? Has anyone tried something similar? 

And for your viewing pleasure, here's our baby:

[Willow and J]

You are so kind!! AD is a hard disease, we realize, but other than that, Willow's very healthy happy one. As long as symptoms are managed and Willow doesn't have to suffer too much, we're good. I just wish there were more things I could have done earlier.