Even some adults have a problem believing there are bad teachers. The most important step in determining if this is a problem is to listen to your child, talk about it and you will discover if this is the case. If possible speak to other parents and find out if their children are having similar problems.
Even if you are still unsure your child has a bad teacher there is evidently a problem. Visit the teacher and discuss your concerns. Most likely you'll be able to tell if it is merely a conflict of character or if the teacher is truly lacking in the skill of teaching and dealing with kids.
Whether your child has a bad teacher or not, it is important she learns to speak for herself. The best way to do this is to have her talk to her teacher if she is still confused or concerned about something.
If your child has talked to the teacher and you have followed up with doing the same but the problem persists, it is time to visit the principle. Explain the problem and your concerns then give it some time to see if there is improvement.
If the problem doesn't improve request a conference with both the teacher and the principal. Explain how the problem is still there and that something needs to be done to change it.
If you see no hope, make an appointment with the superintendent and even the school board, if necessary. Take it as far as you have to in order to make changes not only for your child, but for children who will have this teacher in the future.