Words can cut you to the quick, but sometimes the silence hurts more. With dealing with bullying situations, standing by is almost as bad as participating. Standing by, and not speaking up, is giving tacit approval, and giving the aggressor what she wants: power. It perpetuates the behavior and can even cause it to escalate.
Giving voice to your concerns or speaking up about bullying behavior is not easy. There is the possibility (or the fear of it) that you will become the next victim. It is also hard to stop something when it seems that everyone is involved, but chances are there are others that are also uncomfortable with the situation. Voicing your concern can help others do the same--and perhaps shut down the behavior entirely.
In a previous post, I mentioned how I had been bullied a few years ago. It was seriously the most painful time of my life--even worse than teenage years because I was an adult! This should not be happening to me! This stuff is for kids!