This girl probably has borderline personality disorder. It might sound crazy, but in her head it all makes very logical sense and she is feeling very intense emotions and feelings of rejection. She is desperate for any response from the guy. No, this is not “normal girl stuff”. Many teenage girls have borderline personality tendencies and traits, but they are able to work through it and move on as they grow up. And it is usually never this severe. This girl needs some therapeutic help. I think its sort of sad that everyone here is being so ignorant about this serious mental disorder. If you know someone like this, please keep that in mind, and try to compassionately and gently guide them toward seeing a counselor.
Please note: if this happens to you, the best way to deal with the person is to be honest with them and tell them clearly and compassionately that you are not going to respond and do not want to have contact with them. DO take any threats of harm to self or others seriously and report that to the local police or mental health agency. Try to understand that while this may sound crazy to you, they are suffering immense amounts of pain.