... I find Dr. Horn's medical opinion that she stabbed him in the heart compelling. Her rage was up close and personal and she wanted him to suffer. I also doubt there would have time for her to "go get a knife." IMO she had it with her the whole time. It was precisely because of the wound to the heart and the chondrocostal junction--extremely painful and debilitating, that he was spitting up blood almost as soon as he got to the sink, gasping for breath, unable to defend himself.
It all happened much too fast for her not to have had both the knife and the gun with her the whole time, imo.