Career
Duncan signed with Melbourne Victory ahead of the 2013-2014 season. In January 2014, Duncan agreed to join English club N ottinghamshire County after the Australian season had concluded. Duncan represented New Zealand at age group level, appearing at the 2006 Women"s U-20 World Cup finals, and again represented the young Ferns at the 2008 Women"s U-20 World Cup in Chile. before making her full Football Ferns debut in a 0–3 loss to China on 14 November 2006, and represented New Zealand at the 2007 Fédération internationale de football association Women"s World Cup finals in China, where they lost to Brazil 0–5, Denmark (0–2) and China (0–2).
Duncan was also included in the New Zealand squad for the 2008 Summer Olympic games where they drew with Japan (2–2) before losing to Norway(0–1) and Brazil (0–4).
Duncan played for New Zealand at the 2011 Fédération internationale de football association Women"s World Cup where she earned her 50th cap in a 2–1 loss to England in the group stages. She also featured in all New Zealand"s three matches at the 2015 Fédération internationale de football association Women"s World Cup in Canada.