She was born in Randwick, New South Wales and studied nutrition science at the University of Wollongong. Thornton won the 400 m at the 2014 Summer Youth Olympics, setting a personal best of 52.50 seconds to beat Bahrain's Salwa Eid Naser. She ran for the Asia-Pacific relay team at the 2014 IAAF Continental Cup, though the team finished last. She was a relay finalist at the 2016 Summer Olympics alongside Anneliese Rubie, Caitlin Sargent and Morgan Mitchell.