Maybe she was feeling insecure herself. Just step aside and let the words go by just like any other attack. If you talk back, she feels justified in keeping the conversation going. I don't know what kind of lifestyle you lead, but I'll go out on a limb and assume that you have better things to do with your time than deal with a moron.
As long as she's just running her mouth, let everyone else figur out on their own what kind of person she is. If she gets physical, you know what to do.