Onna-bugeisha (though a fairly modern term, I am told, is one of the female warriors of upper social classes in feudal Japan. Women of a samurai family were samurai by birth. In the Kamakura and Sengoku periods this meant women were trained as warriors as well. While it was rare for them to fight on a battlefield (Tomoe Gozen is a good example of an exception to the rule) they were expected to defend their homes, generally with naginata, yari, or some sort of chain/rope weapon to make up for their smaller stature.
So in-case anyone was wondering about what armor for women should look like.. THIS IS IT.