Actually, I'm pretty certain that Miller did that more to address the issues surrounding the Batman/Robin pairing than anything else. I think he's actually stated that he make the DKR Robin female because of all the 'Batman and Robin are gay' innuendo - the idea being, I think, that he was saying to himself 'so they think BM+R are GAY, do they? All right, I'll make Robin an underaged GIRL and put her in the short-shorts, ha ha, and see how much better they like THAT!' He was essentially doing it more to be provocative than anything else - although, in his favor, he did wind up writing a pretty good character. (Interestingly enough, I think if Bob Kane HAD made Robin female and put her in the short-shorts, he probably would have gotten far more outrage than he ever got about the male Robin. Back then, when homosexuality was something polite people didn't think about, the notion of a boy in short-shorts wasn't all that outrageous - after all, little kids wore shorts all the time, and Robin was manifestly a kid for quite a while there, even if a somewhat older one - but a girl showing her LEGS? Outrageous! There would be letters to the editor! It was only after Wertham started stirring things up that people started to think things might be a little weird there.)