It doesn't take much. Seriously. Just give a moderately attractive chick a gun (the larger the better) and she magically transforms into some hot warrior. It's probably the Tomb Raider effect.
Even if she has a name like Wendy (like this chick). Toss her a low-cut blouse and a Desert Eagle and you're all set! Maybe some Michael Bay-esque explosions and you're well on your way to a Transformers movie.