Hmm. Scene one and scene three have the same effect. I would say she has charging basic or more and she is taking a unarmed attack along her path. Since she never ends up with the gun (or keeps it) i would not call this a disarm. You can add any flavor to the attack as long as she does not end up with the gun.
I would do it as a disarm, some sort of disarm attack trick as Sletchman says as she does actually take the gun off him. Both in the animation and in the game. In the animation she then drops it, which is an option in the game. So attack-disarm then free action to drop and flee. Or some sort of posturing as Krensky suggests.
I like some of these suggestions, And thanks for this thread Mister anderson, as most MC unarmed combat is now going to look more awesome in my head now
Man, this is really making me want to go play that game again, it was so much fun doing all that stuff