The deaths in the movie are all crafted in a way that evokes a sense of repugnance.  Compared to Anton, his victims, with few exceptions, are as helpless as worms fighting eagles.  Carla Jean was helpless like this.  And the repugnance comes not from her death, but from the initial hope that she may have lived and the resulting shock of Anton checking his shoes, presumably for blood, after leaving her house.

We’ve already seen him kill the helpless.  The scene is meant to first give us hope about his possible mercy, and then crush us with his savage ability to follow through with his previous ultimatum.

I think her death matchs that scene perfectly.  Carla refuses to call the coin flip, she refuses to give Anton the validation of feeling the descision has been made for him.  He has already made his descision, but he wants to feel that it is ultimately out of his hands.  Just as she does that, the directors refuse to validate our uncertainy about her death.  “Did she die? Didn’t she?” Just as with Anton, we, as the audience have initial ambiguity, even though we really DO know.  We don’t want to believe we know; that we can understand the actions Anton is capable of.  We want him to remain a completely alien monster.

In that respect I think it’s a brilliant move.  The directors have managed to make us feel shocked and repulsed by the lack of the concrete, not just by Anton, and also by ourselves.  The scene could almost be described as a metascene.  It’s a scene about a scene of murder.  We don’t need to see it to know it happened.  Knowing a murder happened and not seeing it doesn’t make it have any less impact.