I had my dd's primary care physician refer us to a nutritional counselor/dietician who specifically works with kids/teens with medical issues and food intolerances/allergies. She talked to both of us, but mostly she addressed dd personally. She talked about the diet changes that would be necessary, and she talked to dd about what she likes and doesn't like. Together (I mostly took notes) they came up with some ideas, foods to try, etc. She made sure dd understood what she is intolerant to (it can be hard for a kid to grasp what MSG is). We went shopping together and now dd is more able to keep track of her calories, fiber, etc. The nutritional counselor recommended some specific nutritional drinks like Ensure Plus.
When you're born with an allergy or intolerance, you don't know any other way of eating.
But when you're old enough to have your favorites, and have friends, and you know you love McDonald's chicken nuggets and all of a sudden life changes and you can't eat certain things and you know you're different from your friends, it can be a real loss.
So I suggest getting her a counselor who understands food and life changes and how to explain her food needs to her friends (not that she has to explain everything but what to do if one of her friends pressures her to eat something that is forbidden) and the importance of taking care of her health. The nutritionist will have menu ideas and can help you figure out how to feed your family without losing your mind.
I too did a ton of research (our issues are: dd needs easily digestible foods, high protein, high sodium, no certain fruit sugars -- it's complicated!!!) but having a professional explain it really helped. We had an hour long evaluation with the nutritional counselor, and dd will have a follow up appointment every 3 or 4 months. That way we'll make sure dd is getting enough calories, nutrients, etc.
Good for you for doing all the research! Make sure if you do see a nutritionist that you are clear about what the problems are, and that you take good notes and write down all your questions beforehand.