Food allergies someone please help?

My daughter breaks out in hives and has trouble breathing when she eats fish, or rhubarb. She has eaten popcorn shrimp, fish sticks, strawberry rhubarb jam, and had this reaction most recently she ate one french fri that was fried in the same grease as the people we were eating with (they had fish and shrimp) and she broke out from head to toe.... but when i take her to the allergist they do all there testing and they say she is not allergic to fish... someone please help me figure out whats going on because they don't seem to want to... they say that she is allergic to soy but yet she eats chinese food and other soy based products all the time and nothing ever happens to her....