What should you do in the following case?

As an administrative assistant, you have been training Mrs. W., who is not directly under your supervision. She has not appeared to be particularly competent during the month she has been in her position. You are explaining application procedures to a client when Mrs. W. interrupts to ask you a question. You tell her you are busy with a client and will come to her office when you are through. In a low voice, she begins to call you names and say bad things about the department. There are several clients in the office in addition to the one you are working with. The supervisor doesn't appear to be around.