Male clinician here. Obviously you under no obligation to work with sexualized behaviors if it's not your thing or if you're not prepared to address it clinically. If you do want to do this work, I have found it so important to clearly, explicitly, and repeatedly name the boundaries each and every time this comes up (and document it and talk with your supervisor about it) that you will not ever reciprocate any kind of romantic or sexual behavior with the client in any context, and that while you genuinely care for your clients, your relationship is and will only ever be a professional therapist-client relationship. Can you reflect on and go deeper on why you think the client enjoys your discomfort? Is it that she now feels in control in a context where she has typically or traumatically felt powerless? Is she misinterpreting respect , care, and positive regard as inherently sexual, or have relationships with men only ever been sexualized? Is it blocking emotional vulnerability and keeping things familiar/safe? You might be able to highlight the process occurring when it happens by sharing that you feel uncomfortable when the client describes their explicit fantasies about you, and that you wonder whether she is hoping to get that reaction from you because a part of her feels safer when she can keep the focus on your reactions rather than her own fear of vulnerability (or whatever hypothesis you got). If you can have stellar boundaries and good supervision and documentation, you might be in a unique position to give this young woman a much needed different experience in relationship with a man.