Annoying lady came to my door and asked for my mother. What?

I'm 37 years old, married, no kids. I was at home one afternoon (husband was still at work) and a lady came knocking on the door. I opened it and she demanded to speak with my mother and asked me what high school I go to and when I'm graduating. Okay, I'm a small person, but that's just ridiculous. And no, I don't look so youthful and beautiful, I'm just small and have a SLIGHT young-ish look. I know I should have made a joke to this lady about how I'm way past high school but instead I was a little disgusted because she was so demanding, as if she couldn't accept that I am NOT in high school and my mother does NOT live with me. Aren't some people so ignorant??? What would you have done?