A: It is good that you are concerned about your daughter's level of anger as she enters school and begins to interact with people in the outside world. But the problem here is that aggression is a two-way street. If you are trying to "fight the fight," the result will only be more fighting.
Techniques such as inflicting physical or psychological pain do not work, since they only make children more aggressive and more likely to lash out. Give up the goal of "disciplining" your daughter and replace it with the long-term goal of helping her to grow, over time, into a mature, self-disciplined person. This is an entirely different project, and it will involve you trying to anticipate problems before they arise, remaining patient and calm, and trying to understand and respect your daughter's feelings from her own point of view.
Of course, if she is running into the street, you have to overpower her and pick her up to prevent a life-and-death situation. But most situations do not involve danger, so you cannot successfully force your will upon her. Instead, most situations are conflicts that require interpersonal skills to navigate. You may benefit from learning new skills to negotiate more constructively with your daughter, to solve problems together as a team, to keep the mood friendly, and to figure out what is upsetting her. A family therapist, counselor, or other mental health professional may help you here. As the first step towards addressing what is troubling your daughter, ask your pediatrician or family doctor for a referral for a comprehensive evaluation.