I would suggest that it is manipulative because the therapist is not responding: she is reacting. Professionalism requires a therapist to be reflective, not reactive. There seems to be no reflection psychologically, but simply a reactive action (which can easily be seen as punitive) which only focuses on the therapist securing payment. Even if the OP has a history of non payment--which I see no indication of in her post--the therapist's job rests on addressing the issue psychologically; it is this which distinguishes the therapist from most other professionals offering a service for a fee. If she is unable or unwilling to do so, she shouldn't work with the client. And I would repeat that APA speaks to these sorts of issues and always keeps the ethical duty to reflect, not react, as a central tenet.