It's interesting to contrast man/girl relationships in, say, classical Athens with male pederasty in the same time and place. Ancient Greek pederasty ostensibly had an educative purpose: a boy needed to learn manhood from an established, virtuous (note the etymology of that word) citizen. In contrast, men coupled with fertile adolescent girls to perform their reproductive duties, AFAIK without any interest in educating or socializing the junior partners to the marriage (at least, that interest didn't exist on the cultural level: I'm sure some individual men instructed and socialized their girl-wives, even if the latter couldn't become proper citizens). With girls romantically and intellectually neglected by men and socialized primarily by women, I'd hardly be surprised if woman/girl pederastic friendships were commonplace, unbeknownst to men. I could see the same thing happening in Ottoman harems or other segregated, strictly female spaces--although as you point out, it'd be hard for us to recover any traces of that stuff now.