This woman needed a FAR longer sentence than she received, but I think killing her is a step too far. If we allow ourselves the sort of rage which caused her to kill a man, then we lower ourselves to her level, and additionally any positive contribution she could have to society is prevented. Suppose she does it again? Then I'd consider killing her. As it stands, she is a wretched human being, but a human being nonetheless. As far as I understand it, the justice system is about the betterment of humanity. Killing someone who could be reformed into a positive influence does not sound like the betterment of humanity to me.
PS: This has veered dangerously off the LGBT thread's topic. Might I suggest starting a thread on ethics wherein we may fight to the death over our moralistic viewpoints?