“You can judge a society by how well it treats its prisoners.”
The purpose of any societal sanction against law breakers should be to stop the offending behavior and rehabilitate the offender for reinsertion back into society as a productive member. As horrific as her crimes are, her death at the hands of the state would only serve as an example of death as an acceptable solution to solve a problem. This is a prime example of why we are a nation of laws that can impartially assess a punishment free of emotion, as evidenced by comments in this thread.
There are of course some who can never be rehabilitated. They need to be imprisoned for life, unfortunately. Even then, we should be working toward rehabilitating them and making them productive members of society, even if they must contribute from prison.
FBI serial killer profiler Robert K. Ressler was opposed to capital punishment for practical reasons. Given enough time, almost every killer will open up and reveal their psychology and their techniques which can be used to prevent future crime. The death penalty is more expensive, isn't a deterrent, and serves no purpose. A truly civilized society will not kill its citizens.
With great freedom comes great responsibility.