I am so very sorry to hear that your granddaughter has had to endure such horrendous treatment. I believe that the chronic and severe nature of the bullying requires a very strong response.
 
What has been the response of the school, school board, and superintendent personnel to date? If you remain unsatisfied with the response of school personnel, I believe that you should consider contacting the police. Your granddaughter is very lucky that she was not hurt more badly in the incident in which the teens threw things at her. She could have been hit on the head, which would have had catastrophic consequences. Thus, please do not hesitate to involve the police. This form of bullying must stop.
 
Finally, given that your granddaughter has had to suffer with bullying for such a long period, I believe that she is greatly at risk for physical and emotional difficulties. As you may know, children who are bullied are more likely to experience physical ailments (e.g., stomach upset) and emotional distress (e.g., depression, anxiety). I recommend that your granddaughter's school provide some sort of counseling support for her, whether at school or outside of school. She will need ongoing support to deal with the blow to her self-esteem. Also, you didn't mention whether she has friends at school or outside of school. If she has difficulty maintaining friendships, the counselor can help her sharpen her social skills. Research shows that at least one supportive friend in situations like this can be very beneficial.
 
Best of luck to you and please continue to fight on your granddaughter's behalf. She is so lucky to have you in her life!
 
L. Compian, Ph.D.
Counseling Psychologist
Education.com