I do know that her chances of outgrowing the allergy are a lot better if you don't feed her anything she is allergic to. Have you tested your other daughter? She may be allergic, also, and it would be better to start her on the same diet now. If you do she may outgrow it by the time she is your older daughter's age.
I am taking care of a 22 month old that was allergic to soy and milk, but after sustaining use she is only slightly allergic to milk. She was still showing signs of allergies, so they tested her for a few other foods and found she was highly contagious to corn. We were so happy about the milk and soy that we didn't even realize for awhile how many things corn was in....it is worse than milk, but we are working through it and hopefully she will outgrow this allergy soon.
We looked up information on the internet and printed off a list of items she couldn't have...this helped us a lot.