Virtual Reality (VR) Serious Games can improve physical, cognitive and mental rehabilitation by helping patients stay engaged and entertained while performing rehabilitation exercises. Patients need therapist monitoring and intervention tailored to each patient and to each point in their unique rehabilitation process. This article reports on a prototype development of a therapist interface for an occupational therapy rehabilitation VR game, which was guided by user research and co-creation sessions. Usability testing was carried out with low-and high-fidelity prototypes. Despite achieving a System Usability Scale score of 93.75, the interface requires further development at the level of game-session creation and parameter personalization. This article showcases relevant challenges in interaction design for including the therapist in the patient's game-playing while allowing fast/efficient setup of appropriate game-based therapy, thus balancing patient outcomes and efficient use of therapist time and effort.