How would you deal with this?

Well for one you are not wrong you do have a point. But then again don't sweat the small stuff (that is my favorite quote). You have to come to the point in your life when you realize that some people are just miserable with their lives and cannot control it. Some people wake up upset and go to sleep angry and their whole goal in life is to encourage everyone else who pes their way to be angry like them. She succeeded with you because you got upset. In reality she was wrong but on the other hand, it was just two minutes. Don't let people like that rent space in your mind. Next time it happens smile and get off that will bug her more than arguing with her.