This is because they never believe they will be the one that wronged someone until it actually happens, or that they will escape punishment if they do. They are completely unwilling or unable to put themselves in the other person’s shoes. Certainly, that’s harder in this particular case. As for the escalation that inevitably happens with vengeance, which is why justice started with the concept of “an eye for an eye”, this just means it gets worse. We are, or should not be at this point, at the brink of civilization. We have more resources and tools to guarantee that justice is reasonably served and society is safe without having to put people to death. People who see that as a viable or even necessary option need to reevaluate their concept of the value of human life. Lack of doing so or being taught that, which this murderer certainly didn’t get early enough in her life, is the root cause of a lot of these situations, and is not a solution.