A six-year-old girl with Rett syndrome was assessed in a multi-disciplinary specialist therapy clinic and aspects of her responsiveness and developmental potential were found in the music therapy assessment. Functional hand use, eye-referencing, motivated and intentional communication were observed and reported through video analysis of a 30 min session of music therapy employing improvisational methods. Absent or reduced hand clasping/plucking, interactive turn-taking, primary and secondary inter-subjectivity, and vocalisation with appropriate emotional expression were evident. Stable truncal positioning and occasional gentle restraint of either hand improved both spontaneous and prompted activity.