I was under the impression (and by impression I mean I have no idea where I read this and thus cannot back up anything I say) that the problem was at the second

I was under the impression (and by impression I mean I have no idea where I read this and thus cannot back up anything I say) that the problem was at the secondary schooling level; girls started out with a healthy interest in science and engineering when they begin at 11 or 12, but that interest level rapidly decreases as they move through schooling. The question is what is happening in the way we're teaching girls that they get so turned off by it? Obviously its not innate, because as you note, there used be a lot more women graduating with CS. I guess there could also be a societal argument as well, but I wouldn't know enough about the cultural norms of 1990 to comment.