If anything like this happens again, chuckle, pat her very gently on the top of her head, turn to your friend with one of those indulgent "oh aren't they so cute at this age" sighs, and then completely turn your back on her.
This happens to me all the time. Even when I was in grade school. I was always picked on because I always used to brush my hair straight and it was POOFY. And now, it's curlier and people still look at me weirdly and whisper to their friends.