Heiner was born in Shellharbour, New South Wales on 15 May 1987. She took up running seriously in 2002; as a 17-year-old, she represented Australia in the 1500 metres at the 2004 World Junior Championships in Grosseto, but was eliminated in the heats. At the Commonwealth Youth Games in December 2004 she won gold in the 3000 metres and bronze in the 1500 metres. In 2005, she was Australian under-20 cross-country champion and placed 16th in the junior race at the World Cross Country Championships in Saint-Galmier. She competed in the World Cross Country Championships again in 2006, this time placing 18th in the junior race, but missed the IAAF World Junior Championships later that year due to an injury. She studied pharmacy and did not return to the track after recovering from the injury.