Why is everyone so mean 2 her?

The best thing you can do for her is be her friend. Middle school is hard time, and having a real friend who genuinely cares can be the most helpful thing. I would suggest that if you are concerned that she may want to harm herself, or already is, that you tell a responsible adult immediately. While this may breach her confidence in you, it is best to protect her from herself then it is to keep a secret.