N.,
I would suggest you check her environment. While I know you work at her school, how often do you observe her class? My sister went through a similar behavior change when she was 3 and my parents found out that her teacher had been talking to the children the same way my sister did (Sit down, shut up, bad girl), etc.
Her behavior sounds violent, not ADD. ADD children are usually just easily distracted but not mean. SHe could be acting out because this is the only way she can get your attention to explain a problem going on in her life.
Another thing I will suggest is that you speak to her about appropriate and inappropriate touches. Children who have been "bothered" also experience a behavior change that is negative because they can't explain it anyway else. I know all this is scary to think of but when it comes to my children I beleive in better safe than sorry.
I have had children in my family who had tubes and tonsils/adnoids removed and never did they expereince a behavior change for the negative...rather the opposite occured. I hope this has been helpful!