Abstract: Introduction: Contemporary music therapy interventions involving autistic children frequently take family-centred approaches, which seek to situate and inform the therapeutic process within a child’s wider family life and environment. Despite this, there is limited research into how music therapy can facilitate the development of relationships between family members. This paper presents an interpretative case study of a series of music therapy sessions with the family of a 9-year-old autistic girl (“Anna”). An adapted music notation, Figurenotes, using symbols employing colour and shape to represent pitch and duration, was used to facilitate music-making by family members on piano keyboard and tuned percussion instruments. Method: Qualitative data was collected, consisting of transcriptions of video recordings from sessions, researcher notes, and a parent interview. Reflexive thematic analysis, an approach that highlights the researcher’s active role in knowledge production, was conducted with these data. Results: Four themes emerged: (a) Shared music-making, providing a new way for the siblings to relate to each other; (b) Anna’s leadership in family music-making; (c) Independence of the family in playing music together; and (d) Usefulness of Figurenotes as a shared resource. Discussion: The themes offer insights into the mechanisms of change within family music therapy and the utility of Figurenotes as a therapeutic tool for facilitating musical engagement and social interaction. This study demonstrates how shared re-creative music-making can improve relationships within families involving autistic and non-autistic members, expanding the scope of family-centred music therapy interventions beyond individual client goals.