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-20cross-country champion and placed 16th in the junior race at the World Cross Country Championships in Saint-Galmier. She competed in the WorldCross 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. In the summer of 2013, actively working as a pharmacist while also continuing her studies, Heiner decided to resume running. She joined the training group of coach Adam Didyk; her first race back was in January 2014, after a hiatus of almost eight years. Her times improved rapidly, and she met her initial goal of qualifying for the 2014 Commonwealth Games in Glasgow; she represented Australia in the 3000 metres steeplechase, placing fourth in a personal best 9:34.01. Encouraged by the good results, Heiner continued her comeback with an eye on the 2015 World Championships in Beijing and the 2016 Summer Olympics in Rio de Janeiro. She became Australian senior champion for the first time in 2015, winning the 5000 metrestitle; the race was held at the Sydney Track Classic rather than as part of the main championship meet, and Heiner placed second behind Kenya's Magdalene Masai but was the top Australian in 15:21.09. She was briefly the 2015 world leader in the 3000 m steeplechase after winning at the Melbourne Track Classic in a personal best 9:31.03. She improved her times further at the Diamond League meetings in Doha and Rome ; the latter time ranked her second behind Donna MacFarlane on the Australian all-time list. Heiner was selected for the 2015 World Championships in both the steeplechase and the 5000 metres. Heiner was selected for the 2016 Summer Olympics in both the 3000 m steeplechase and the 5000 metres. She placed seventh in the steeplechase final with a personal best of 9:20:38 and tenth in the 5000m final with a personal best of 15:04.05.
