Football Ferns coach Andreas Heraf has come under fire for his comments after the sides 3-1 loss to Japan in Wellington on Sunday.
"There are better people out there surely who actually believe in New Zealand getting better," she said.
Duncan has played 119 games including draws against Japan in 2008 and 2013 and was also involved in two victories against Brazil in 2013 and 2015.
"If the coach is not believing in us and telling us we can't go out there to do our best as individuals and as a team, and at least compete and try to win games, then what is the bloody point? You may as well not turn up," she said.
"But in a way, they're powerless because they can't say much to the media because they're under contracts, and I've been there."
"To have such a defensive mindset and to talk about conceding eight is just plain rude and disrespectful to the girls," Duncan told Stuff.co.nz.
"There's just no faith in the girls.
"If that's your attitude then what are you doing there? What's his purpose if he's not believing in his team?"