It’s uncertain, as far as I know. Some online sources claim that it’s Nakazawa Koto, others say Nakano Takeko. It’s not unlikely that it’s neither. It may be just an unimportant Onna-Musha of the Meiji period, or an actor. It is an accurate depiction, so if it is an actor, she’s wearing actual armor of the sort that would be used by an Onna-Musha.