How to have my voice heard?

So there's a very mean hall monitor/janitor at my school. She is accusational, mean, and unfair to all students even those who do nothing wrong. She lies and humiliates students in front of teachers and peers. I wrote a very professional letter about my as well as other students issue with her because it seems as though the school is completely unaware. I'm a little concerned that even if I give this letter to my principal or superintendent, that nothing will be done. This is because since she is so mean and nasty to us, students tend to be disrespectful back because we are being treated so poorly with no reason for it. We need our voices to be heard and something to be done about this. Any suggestions for the best result? Thank you!