I have to say, the whole storytelling convention of a woman dressing up as a man, either to go to war or to hide from the Lannisters or to do whatever else the character needs to do, has always struck me as more than a bit untenable. There are just basic bone structures and other bodily shapes that I feel sure would give away all but the most naturally androgenous women.
Well, turns out it wasn't just Mulan, there are at least 250 documented cases of women--straight women, who had successfully lived up to their culture's standards of femininity their whole lives--dressing up as men
to fight in the Civil War. And many of them did it not because they wanted to fight, but because it gave them an easy opportunity to attain the same societal rights as men.
Some weren't even discovered until decades later when they were dying in old soldier homes, the predecessor to VA hospitals. The article's pretty interesting.