Gary Meers, Ed.D.

Elizabeth,
First you talk with her privately and let her know that this behavior is unacceptable. In fact you can ask for her help in not interrupting the class because you are sure she does not want to interfere with the learning with others. If that does not work you can tell her in class that you will not allow her interruptions. If she does not cease the behavior you can let her know that she will be removed from the class because she is not contributing to the discussion of class topics and is taking the course off track. This puts her behavior and future in the class in her hands. Make sure to document everything you do and say with her in case there is an issue later on.
Gary

Gary Meers, Ed.D.