Would it be inappropriate to bring my friend in to one of my therapy sessions?

So her friend need counseling? Well, she can talk to your therapist if she is a client. She needs to establish a client relationship. To make it simple she need to pay for herself. She can't use your session for herself as it is unethical. It is also insurance fraud. What kind of hard core question? Why can't she talk to her teacher? Is it murder?