Sudden Lip Swelling & Blisters???!!!?

My sister just called me and said that on her lunch break she ate her typical favorite meal at Chipotle (she ate nothing new to her control). As soon as she finished her meal and was leaving, her upper lip began to swell and two blisters formed on her center upper lip on the inner part. She said they are not painful, more numb feeling. I could not find anything online except food allergic reaction - which it should not be if only what she ordered was put in the burrito. What could this be and what should she do?