Here's the entire deleted scene:
I think the original decision to delete this scene was the correct one. It adds confusion, since we don't know much about the species at this point, and providing this sort of info this late in the movie slows the pacing. And for suspense purposes, it's better if we don't know anyway.
Another issue is that you don't really want your story's hero intentionally killing any good guys. It muddies the waters, morally speaking, and it brings the hero down a few notches in the viewer's estimation. Sure, Dallas begged her to do it, and yeah, it was a mercy killing, and necessary, but still. Heroes don't fry good guys with flamethrowers. This scene did more harm than good, so it was wisely cut.
So I won't be watching that version anymore. Just the theatrical version. Which, of course, is pretty awesome, and almost as cool as the sequel.