It's a common (and tiresome) critique of historic or fantasy novels that place women in pre-industrial military roles that such a character and activity is simply implausible. "Women couldn't do the work." "A long-term disguise as a man is not believable." And so forth at tiresome length. The best counter to such critiques is to drown them in data. Alas, even that approach won't satisfy the more stubborn of the nay-sayers.