With five days to go until the election, she had little new to offer on the campaign trail. All the policy has been rolled out, and her stump speech is now familiar.
That didn't matter to her supporters. One, a middle-aged woman, broke into tears after getting a hug from the Labour leader in the town's Majestic Square.
At the RSA, another supporter asked her to sign a Wonder Woman poster. A pharmacy closed for an hour so its staff could come and hear her speak.
"I'm really sorry to anyone who had a prescription to pick up," Ardern said.
She ran into Colleen Garrett, a childhood friend from Morrinsville College.
Garrett recalled a 16 year-old Ardern speaking at their school after she had visited the Beehive. She knew then she would be Prime Minister one day, she said. "She just had it from the get-go."
Ardern spent a precious day in the town because it is a marginal seat. National MP for Whanganui Chester Borrows is stepping down at the election and the electorate is up for grabs.
Labour's candidate Steph Lewis, the daughter of a prison officer, said Borrows' 4500-vote majority in 2014 was now irrelevant.
"There's a mood for change," she said. "People like that I'm young (29), that I'm part of a generational change."
News trickled through from Morrinsville about the farmers' protest. One of the farmers had held a sign calling Ardern a "pretty communist".
"Did they intend that to be a compliment or an insult?" Ardern asked reporters. "I'm not sure."
She began the day at Whanganui City College, whose alumni included the late Sir Paul Callaghan. Lewis was dux there a decade ago.
Principal Peter Kaua said the school had hosted John Key when he was Leader of the Opposition in 2008.
"There was a huge gust of wind and John Key didn't miss a beat. He said 'the winds of change are nigh'. There could be changing winds for you, too."
Ardern asked who was interested in politics, and just one student put up their hand.
A boy at the back asked if she hoped to be Prime Minister one day.
She didn't miss a beat: "I'm hoping to do it ... in five days, actually."