C..
Instead of focusing on *punishing* her I would focus on changing her behavior using discipline and guidance. Talk with her. Ask her why she did what she did. That's the first step in getting her to think about her actions BEFORE she acts.... First you have to get her think about what she already did.
You need to make it clear that there are other, healthy ways to express how she is feeling. Make HER come up with alternative behaviors that she can express when she is angry or bored.
Before school - talk with her about these options. When she gets home talk with her about the decisions that she made that day and let her know you are proud of her when she behaves correctly.
Let her know the consequences of her actions are that she won't have anyone who wants to be her friend and school if she does not treat people correctly.
Is this a CHANGE in behavior? If so, you need to find out why. kids don't just all of sudden start basically assaulting other kids without a reason. So, find out what is going on in her world.