What Causes Hives While On Symbicort?

My wife is experiencing severe hives. She has been tested for food allergies, and we have avoided soy and eggs (they raised a bump on her skin during the allergy test). The asthma/allergy doctor took her off of singulair and yaz birth control stating that orally taken medicines will cause hives before inhaled medicines. The only other medicine she is consistently taking is the symbicort inhaler (two puffs in morning and two puffs in the evening). This is the first time she has ever taken symbicort. She has been on it for five to six months. Could this be what is causing her hives? I feel we have eliminated everything else it could possibly be.