Being punished by the law and being put to death are only two ways a person can be punished. Trust me, as popular as this case has been, do you think she will ever be able to get a job? Even if her parents keep supporting her, they won't live forever. Eventually Lee will get married, and have a family of his own. Do you think he'll want her around then?
What about her friends?
One way or another, the life Casey once new is over. Things will always be tough for her, and people will walk up to her probably for the rest of her life and call her a baby killer. Trust me, she won't get off free and clear, and resume her normal life. That's what she's hoping for...it never works out that way.