Muir grew up in Oxford, and attended
Cherwell School. She began playing rugby in Oxford at a young age, and joined the Oxford Harlequins (U6-U11) and then moved to the Gosford All Blacks, joining the U15 and later U18 sides. She represented the South West at age grade level and moved to the Wasps' Centre of Excellence before joining the senior team. She was awarded a Brunel Sports Scholarship, allowing her to train as a professional athlete while studying a sports science degree. Muir played cricket until she was 12, partly because her mother preferred watching cricket to rugby. She was an excellent fielder but only an average batter. In 2025, she hosted a workshop with teammates
Ellie Kildunne and
Lucy Packer which aimed to "inspire the next generation of female players at Chinnor Rugby Club in
Thame,
Oxfordshire." ==Honours==