Beyond black or white, you also gotta think that the person who made that comment was a teenager... they say some really stupid things. Hell, when I was a teenager I said such stupid things! I'm embarrassed to even remeber them. So what you did (i.e. turn away) was, I think, spot on. An alternative would have been to sit down and explain all what you have said in the post to her, but that would have taken time and a supernatural ability to control your emotions. But it would have probably taught her not to be so gratuitous with her comments - kids say whatever comes to their mind and it often takes an adult to tell them when they are out of line.