She confirmed there will be 16 Labour and four NZ First ministers in Cabinet, with three Green ministers and five Labour ministers outside Cabinet.
She said there was a lot of work to be done, and she would take time to "reflect on this moment and indeed on the campaign once Christmas arrives".
She found out the news while watching Peters' press conference last night, but had a sense early on that he was going to choose Labour when he started talking about economic prosperity for the benefit of all New Zealanders.
Asked about being labelled a coalition of the losers, Ardern said: "Obviously I would characterise that as unfair. This is an MMP environment. We formed a coalition Government based on a majority of votes and based therefore on what a majority of New Zealanders sought this election."
Asked about moving in Premier House, Ardern said no decisions had been made, but she went home to her Wellington apartment last night and had a "pot of noodles".