It doesn't pretty anything up, what you have to realize is, you can treat the symptoms, or you can treat the symptoms and the cause. If you ignore the cause and only treat the symptoms, at the end of the day, your still sick. One way or another, the teenager is a victim. She still needs to be punished for her actions, and even if she was sentenced to death, she would still be a victim of something which we may never know. We are all victims of the devil and sin passed on to us by adam and eve. I am not giving an excuse for what the girl did, but if you don't look at the things in society that cause these kind of problems, at the end of the day you still have the problem of more and more younger children commiting more and more terrible acts.
Also, with abuse, If one abuser abuses 25 people, those 25 people suffer and because of that 100 people become affected and suffer and are scarred by those 25 people and the cycle continues. If you stop the abuser from abusing 5 people, then only 80 people become affected. Do you follow the logic?