Actually, Leia would have the upper hand in a fight, due to having a gun, which is not only a real weapon, but a ranged one nonetheless. Not to mention the fact that she's a good shot with one. In order for Tifa to gain the upper hand, she would have to dodge Leia's shots, get in close, and disarm her. And even then, I doubt Tifa would kill Leia. Tifa seems like the kind of person that would only kill someone if she had a really, REALLY good reason to. She would only knock her unconscious, or as Dacon puts it, "rough her up a bit". Though I suppose in a catfight there are no weapons, so Tifa would have the upper hand beacause she knows martial arts, and as far as I know, Leia doesn't.