But Ardern, speaking at her post-Cabinet press conference today, said she had been told she would be one of several interviewees.
"I generally have a bit of a policy of not really engaging in any efforts to write anything specifically of that nature - about me."
She has, however, agreed from time to time to contribute to books about women and leadership.
"That was the nature of the request I received in this example."
The approach was in 2019, and she was told she would be one of 10 political leaders to be interviewed.
"On that basis, given it was not specific to me, I was happy to contribute."
Asked if she had been misled, she said: "Clearly I was."
She would be seeking that her statements were not misrepresented in any way in the book.
"And certainly the claim that it was an exclusive interview for the purpose of writing a book of that nature is not true. I will certainly ask for that to be clarified."
Vani told the Herald there had been a misunderstanding.
"We (me and my co-author) never said that I interviewed her for her biography. We have always said that it was a project that I was personally doing to interview women leaders.
"After interviewing Jacinda Ardern, we felt that she deserves a complete biography [rather] than a chapter about her. It was our personal decision to go for a complete biography."
Vani added that it isn't an authorised biography.
"So the Prime Minister is right. I interviewed her for a project on women leaders and I was personally so moved by her compassion that we felt it deserves a complete biography to share with the little girls all over the world. It was completely our decision.
"We decided to go with Jacinda Ardern exclusively as I felt the same compassion in her as I have sensed in other women Nobel Peace Laureates whom I have interviewed for my previous book, Battling Injustice:16 women Nobel Peace Laureates. It's her compassion which moved us to share her story."
Ardern also repeated her discomfort with the proposal for the They Are Us film, but would not share an opinion on whether the film should go ahead, or whether it should receive any state funding to help its production.
"It's not for me to say what projects should or should not go ahead. It would be seen to be wrong if I intervened in that way."
Ardern is Associate Minister for Arts, Culture and Heritage, and Cabinet Manual rules state: "No Minister should endorse in any media any product or service."
Ardern added that no state funding for the project has been requested.
"It's still a very raw event for New Zealand, even more so for the community that experienced it. I agree there are stories that, at some point, should be told from March 15 but they're the stories from our Muslim community.
"I don't consider mine to be one of the stories to be told."
Today Kiwi producer Philippa Campbell pulled out of the project, following the huge backlash in recent days.
"I've listened to the concerns raised over recent days and I have heard the strength of people's views. I now agree that the events of March 15, 2019, are too raw for film at this time and do not wish to be involved with a project that is causing such distress.
"When I was approached to work on the film I was moved by the film-makers' vision to pay respect to the victims, their families, and those who assisted them.
"This was reinforced by research interviews undertaken by producer Ayman Jamal with members of the Muslim community in Christchurch. I also hoped that telling the story of swift gun control action might resonate in America and other countries that have struggled to create political consensus to control guns.
"I deeply regret the shock and hurt the announcement of the film has caused throughout Aotearoa New Zealand."
Campbell said the announcement was focused on film business, and did not take enough account of the political and human context of the story.
"It's the complexity of that context I've been reflecting on that has led me to this decision."
