T.G.
Wow! Sounds like you are talking about my 5 year old girl!! I know how you are feeling right now. My daughter just finished with another one of her tantrums.
We handle school a little differently. When she does not come home with a green light the first thing I do is find out why. Recently is was for running in the library after being told twice not to. I asked her why she thought the teacher asked her not to run. When she answered correctly I asked her why she ran. Of course "she wanted to". She had to draw an I'm Sorry picture (because she doesn't know how to write yet) and I gave her a choice of loosing her 15minutes of tv before nap time or her outside play time. The next morning we went to the teacher together and she had to appologize for her actions and give the teacher the picture. In front of her I told the teacher that I was not happy with her choice to ignore the teacher and that she had to loose something. Privately the teacher thanked me for following up with her at home because most parents do not.
Now at home, words can hurt! I hear "I hate you" and "you don't love me" quite often. She throws things, kicks the wall, slams the door into the wall etc when she has been put in time out. I had a consult with her pediatrician and I was told that some children go through this and it is worse that others. They said to be patient and consistent with punishment.
One thing that I learned that helps is that when she is acting out, I stop her immediately and send her to her bed. I actually say, "go sit on your bed until you can get control of your self". My daughter acts out most often than not out of frustration. She does not know how to convey her thoughts and feelings about situations to us. During the fit, it is very difficult because she is screaming and throwing things. I do not engage in conversation with her until she has calmed down. Once she is quiet i tell her I will set the time out clock ( 1 minute for each year of age). If she starts again, I stop the clock. I restart it when she is quiet.
I have used rewards, I have taken all her toys away and made her earn them back, she has no tv in her room, she has gone to bed early . . . . if you can think of it, I have tried it for discipline.
I suggest you keep your talk to her simple. Too many words tend to go in one ear and out the other. Try asking simple questions like, "what upset you?" " how would you feel if johnny hit you?" "do you think it was nice to use your hands for hitting?" etc.
If she hurts a child, she should be bringing that child an appology. If she disobeys teacher, the same.
I know it is rough right now, but we need to stay strong and don't discipline when you are angry. It won't be effective. If you need to talk, send me a private email. Maybe we can trade secrets (if there are any left)