I went through a very similar thing in high school and it actually lasted for my entire senior year. I was stalked at school, home, work, threatened to be beaten up, almost ran over with a car, had my tires slashed and even had a knife pulled on me. We didn't have online sites back then...it was the bathroom wall.
We called the telephone company about the phone calls, we spoke with the school authorities about the harassment and even spoke with the sheriff's dept. There are limits to what anyone can do in these situations. It sucks but until a law is broken and you can prove who did it, people will get away with crappy stuff. I remember being really scared at times but mostly angry at the situation--not suicidal. My parents were pretty involved and protective throughout. In my case, it was a spurned loser ex-boyfriend and his new girlfriend (and her friends) causing the problems. They knew what they could get away with without getting into trouble. I had to learn some coping techniques and self-defense/evasive skills. Bullies are a-holes, but there's no law about being an a-hole.
Bless you for what you had to endure. What happened to this girl was horrible and more horrible was that she chose to take her own life. I still cannot believe there is not something more to this story.