That is one way of looking at it I suppose. My assumption was that the chip would not put her in a position where she would have to kill to live, however, she already was in such a position when the chip activated so there was very little to be done. Both shooting at the same time is an alternate explanation though.

Shouldn't it have been shown? I am not a clever man.

We're given enough information to figure it out. Had it been shown the comic would have lost its impact.

But movies pull the same bullshit. I understand it loses its impact, but why not do it in some other way? I dunno, I'm just being stupid.

Because the impact is the point. The whole point of this comic is to kick you right in your balls of feel. If there is no impact there is no reason for the comic.