Heffernan comes from a family of netball internationals: at the 2024 Netball Nations Cup, herself and her sister, Georgia Heffernan, became the third set of sisters to play international netball for New Zealand. Her mother, Annette Heffernan and her aunt, Maxine Blomquist, were the first set. However, the Heffernan sisters are the first sisters to actually play in the same team at the same time. A cousin, Shirley Langrope, was also a New Zealand netball international. As well as playing netball together for New Zealand, the Heffernan sisters have played together in several teams, including the Southern Steel netball team and the Otago Sparks women's cricket team.
In 2016 and 2017, the Heffernan sisters were members of the St Hilda's Collegiate School team that won back-to-back South Island secondary school netball titles. 2016 was the first time St Hilda's had reached the final five stage and final of the tournament.[10][30][31][32][33] In 2016 the St Hilda's team assistant coach was their mother, Annette Heffernan.[10]
Since 2018, Heffernan has played for Southern Steel.[41] On 11 June 2018, she made her senior debut for Steel in a Round 6 match against Mainland Tactix. She joined Steel as a replacement for an injured Dani Gray and received a contract for the remainder of the season.[42][43][44] She was a fringe member of the Steel team that won the 2018 ANZ Premiership.[45][46] However, she subsequently established herself as senior member of the Steel team. She initially played for Steel at wing defence before switching to centre for the 2021 season.[12][19][46][47][48] Her sister, Georgia Heffernan, also plays for Steel.[49][50][51]
In August 2021, Heffernan was included in the 2021–22 New Zealand squad.[53][54][55] She was subsequently included in the squad for the 2021 Taini Jamison Trophy Series, but didn't get on court.[19][56][57] On 12 October 2021, she made her unofficial debut for New Zealand against Aotearoa Men.[19][58] She was included in the 2022 Commonwealth Games squad[59] and, on 30 July 2022, she eventually made her senior debut in New Zealand's opening match against Northern Ireland.[2][60] In just her sixth test, she helped New Zealand win the bronze medal.[61] She went on to represent New Zealand at the 2023 Netball World Cup and was named Midcourter of the Tournament.[26][62][63][64]
Ahead of the 2024 Netball Nations Cup, Heffernan was named vice-captain to Phoenix Karaka.[65][66] During the tournament Georgia Heffernan made her senior debut for New Zealand against Australia. The Heffernan sisters now became the third set of sisters to play international netball for New Zealand. The first set were their mother and aunt, Annette Heffernan and Maxine Blomquist. However, the Heffernan sisters are the first sisters to actually play in the same team at the same time.[7][67][68] On 22 January 2024, Heffernan captained New Zealand in the match against Uganda.[69][70]
