Read Ana Forrest’s response:
A lot of these are just new-student problems. You need to clearly explain appropriate behavior to her, but not in the middle of class. Take some time after class to go over class etiquette points with all new students. Have a sheet of typed etiquette points with you so you can hand them to your student as you go over them. You should address whatever she is doing to annoy you: jangling keys, noisy mat, coming in late—these should all be part of the written sheet you can give to her and discuss with her.
Next, encourage her to focus on her deep breathing, feeling the pose and trying to be free of jerking and thrashing. If she still has a million questions, suggest after class that she take your beginner course or some private sessions with you, so she can get all of her questions answered.
Relax with her (because she will make you a better teacher) and take control of your class. The energy in class is your responsibility, and she does not get to control it or ruin it for the other students or for you. Use the fact that you are not willing to sacrifice the integrity of the class to inspire you to solve this teacher’s puzzle.
These kinds of students are a dharma challenge. By learning to deal skillfully with them, you will take a big step in developing your own wisdom and authority. Breathe deeply to break free when you become helpless and paralyzed by the chaos of such students. Then pull the class energy together with humor and integrity. Enjoy the process.