Hi T.,
My son actually has those same exact allergies plus about 10more. I know how tough the allergies it can be, espcially when you first start figuring things out. You should really pat yourself on the back. YOu sound like an amazing woman.
As for the frosting, I will tell you that at Whole Foods i found an already made frosting from Cherrybrook kitchen just the other week that does have any of the allergens in it. They had chocolate and vanilla. I wish i still had the jar but i froze it and threw out the container. But i know i got it at the whole foods in Rochester at adams and walton. There is the box kind to make your own but i believe calls for allergens. This was pre-made in a cylindrical, small container. but its enough for a normal cake.
i looked for a substitution in my allergy cookbook but didnt find anything specific for cakes. I will tell you that i have made muffins using canola oil instead of butter and its turned out fine. My son is just now turning two so his taste buds are pretty bland considering what he gets to eat.
there is a website called www.kidswithfoodallergies.org. they have a message board you could post on.
last, i saw someone post about NAET. i will tell you that my son goes to a chiropractor and is getting those treatments. he has gotten treated for milk and cheese just recently. we tried cheese last night for the first time (just a little) and today again and so far nothing. I will try larger doses in a few days. He also got treated for eggs. He needs one more treatment to make it go away 100% but it is about 80% gone now. he had eggs the other day and instead of spitting them out immediately, he ate them so fast you couldnt stop him. he had no ezcema, no cramping, just a little diahhrea so that is why he needs one more treatment.
if you ever want to swap recipes, feel free to reply to this post and ill give you my email address. take care and good luck!