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 FIFA 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 Olympics where they drew with
Japan (2–2) before losing to
Norway(0–1) and
Brazil (0–4). She scored her first senior international goal in a 10–0 win over
Cook Islands at the Oceania Women's Nations Cup on 1 October 2010. Duncan played for New Zealand at the
2011 FIFA Women's World Cup where she earned her 50th cap in a 2–1 loss to
England in the group stages. She was part of New Zealand's
2012 Olympic squad and
2016 Olympic Squad. She also featured in all New Zealand's three matches at the
2015 FIFA Women's World Cup in Canada. Duncan first retired in 2017, but then came out of retirement to attend her fourth FIFA Women's World Cup in 2019 in France. On October 11, 2019, Duncan announced her retirement from international soccer. ==Personal life==