Riding in the 15-strong New Zealand team, she finished second-equal in the 85cc class with Queensland rider Joel Dinsdale.
Duncan finished 2-3 and Dinsdale was 3-2 in the two outings.
It was not enough to better the Australians, who took the title by 18 points at the Harrisville track, just outside Pukekohe.
McGoldrick's fellow 12-15 years 85cc class rider, Joel Meikle (12), had a "bit of a mixed bag" on Sunday with crashes in both his outings.
The first race saw a rut propel the Oamaru youngster into long grass trackside but he was still able to finish.
Then he went down on the first corner of his second race before remounting his motorbike and continuing.
His father, Justin, said it was a good experience for Joel to measure himself against an international field.
On the Saturday, he was third overall in the Auckland motocross championships' 11-12 years 85cc class and winner of the 12-16 years 150cc class.
The latter category was contested by only three riders, making it more of a practice ride, Meikle sen said.
"A couple of dramas" meant Mosgiel's Craig Borley recorded a seventh and sixth place at the first round of the New Zealand Pro 7 championships at Manfeild.
The weekend did not start brilliantly as the defending South Island champion blew a brake hose in practice and had a fuel leak in qualifying.
He hopes to better his results at the second and final national round at Ruapuna Park over March 20 and 21, to achieve a top-five finish overall.
With one meeting to go, Borley is third in the South Island competition after five rounds.
He is still racing the Mazda RX7 he began his foray into the category with three years ago, albeit with a couple of gearbox rebuilds.
Borley said he resisted spending money on serious engine work this season, opting instead for a tune.
"It's a bit down on juice but it's still going."
