I agree. She also should die.
We do it to dumb animals, who don't know better and act according to their basic nature.
My argument for executng children criminals, and the retarded is very simple: not executing her is an insult to the hundreds of thousands of children, and goths, and the retarded who never murder anyone. So it's reasonable to assume that even those impacted groups know the difference between right and wrong.
Take a life deliberately? Pay the penalty. No exceptions, no repeat offender.