It seems that angels are genderless ("insipid Gender") - that's why 82 gets upset whenever someone calls it a her. But the more they spend around humans and they take on more and more characteristics of humans including empathy (instead of cold law). One of those characteristics is . . . of course gender. That is why 82 who has come closer and closer to humanity compared to 2, is becoming more and more female.

Or at least that's how i read it.