It isn't about being nice to convicts.
And there are situations where the death penalty makes sense. High-ranking gangsters in Columbia, for example, tend to find escape rather easy. Executing them serves a real purpose. Had the Ceaucescus been imprisoned rather than brutaly murdered, many would have been killed by those attempting to reinstate them. Ugly as it was, their execution served a real purpose. If we find ourselves in a situation where terrorists regularly hijack planes to demand the release of their conviced brethren, executions would serve a real purpose.
But in those cases, the executions - even though they might be attended by bloodlust - would not be simply because killing people who piss you off in a big way feels good.
What bothers me far more than the death of people who certainly deserve it (and I don't have enough of the facts to decide whether this woman is such) is the pleasure it gives others. That is a far more dangerous and moraly illicit pleasure than any drug.