There is this girl in my class and she is really mean to people. She thinks that if she does these mean things that people won't stand up to her or tell a teacher. She and this other girl (Who used to be my friend, but was very rude and mean) were playing a prank on my friend. I saw them do this and I told my friend about it. The girl got REALLY mad. Trust me I'm not going to write what she did, but I stood up to her because she didn't really scare me. She leaves me alone now, but I can't stand watching her do her "thing" to other people. How can I tell her to stop if I don't want her to begin doing it to me again? Should I just take my chances to stop her from picking on other people?

You did the right thing, and good for you for doing so.

Bullies are stopped when people speak up. They never target just one person, they develop a whole net full of fish.

You have put a crack in her methods, and I hope others stand up to her. But, it isn't likely you speaking up for other people will stop her. She will just continue to do her thing when you aren't around.

It is sad to be the brunt of an aggressive bully. Other than reporting her, or speaking to a guidance counsellor in confidence about what is going on, I don't know what you can do to stop her.

Chances are if she is talked to, she will deny everything, but at least she will know that more people know what she's up to.

Good for you for standing up to her something I never had the courage to do with my bully(although my bully was a guy and he was quite a bit bigger than me) although that was in gr.7 and now that were in high school(gr.10)he hasn't done it since(and the fact that he got everyo other guy in the class to do it to was the worst that and the fact he hit me)
So yes you should take your chances to stop her from picking on other people don't be like me and cower out, if you feel that stopping her is the right thing to do than do it.

You know what? Bullies are people that has been bullied on. So whatever you do, don't bully her!

Talk to a teacher is the best way to solve this problem.

You did a pretty good job on standing up for your friends. Keep up the courage!