I've talked to her about it and she can't really articulate why. I'm closer to the nerd stereotype in that I'm on the computer a lot but her mother (my sister) definitely is not. I think it's mostly pop and teen culture still harboring the antisocial stigma. I'll have to talk to her some more.

There is probably some connection with video games, in that boys overwhelmingly play games where girls do not. I don't think the games cause the disparity; whatever it is that draws boys to VGs is what draws them to CS as well.