She said Labour had contacted NZ First late yesterday and advised them that when Winston Peters was ready to commence talks, Labour was ready to meet them.
She had met with her front bench - her top 10 MPs - and senior party officials this morning and tasked her front bench with comparing Labour's policies with those of the Greens and NZ First.
Labour's caucus met for the first time since the election in Parliament this morning.
It has 45 MPs on provisional results - up on 32 last term. Of those, 17 are first term MPs.
Ardern said Labour could offer a good working relationship based on trust.
She said she respected and trusted Peters "particularly as a senior MP with a lot of experience."
She denied she was a shutting the Greens out by deciding to have only one on one talks with NZ First and the Greens, at least in the initial stages.
She met with Shaw yesterday and said they discussed the election and 'forward planning' for negotiations, including preparatory work on where their policies might meet.
Shaw has said he expected to be part of a coalition government this time, rather than simply offer confidence and supply from the outside.
Kelvin Davis said he was happy to cede the deputy Prime Minister role if that was required, saying the main priority was for Jacinda Ardern to be Prime Minister and Labour in government.
She was not expecting to meet Peters when he arrived back at Parliament tomorrow.
Ardern said talks were a mix of policies, roles and relationships.
"Relationships of trust matter."
Asked what concerned her about what Peters might want, Ardern said "I don't have concerns."
"It is a negotiation after all."
She said Labour would not cost NZ First's policies, but would cost out what the overall result of negotiations were to ensure they came within the parameters of Labour's fiscal responsibility pledge.
Ardern said she had been told the public service could take a role by helping to cost policy ramifications of a potential coalition and Labour would take up that help.
Ardern said she would confirm the rest of the team closer to the time.
On Fonterra chief executive Theo Spierings' salary, Ardern said it would "make people's eyes water" and would concern the shareholders.
Ardern can't say who is in negotiation 'box seat'
Earlier, Ardern arrived at a caucus meeting to rapturous applause from her new and old colleagues.
Her first words to the room full of Labour MPs were to express her gratitude.
"It's fantastic to see some new faces," she told the room after the cheers and applause died down.
"It takes a village to run a campaign... and I know you were driving that, so thank you, thank you, thank you."
Labour is now preparing to arrange to meet with New Zealand First leaders.
Ardern said she could not determine who is in the box seat to secure Winston Peters' support - and she won't rule out compromising on policies including a royalty on water use by the rural sector.
National and Labour held caucus meetings this morning as both form teams to negotiate with New Zealand First.
Ardern already ruled out one of Peters' wishlist items - a referendum on the Maori seats.
Like Bill English, she has repeatedly refused to discuss how much her party could be prepared to pay for support partners' promises or which of its own policies it might need to jettison.
In the lead-in to Saturday's election Peters promised to get rid of Labour's proposed water royalty, if he were part of a Government with the party. New Zealand First does support a charge on water bottlers but not on farmers or the rural sector.
This morning on the AM Show Ardern was pressed on whether she could agree to scrap or alter the proposed water royalty, and again refused to disclose such positions to media ahead of any conversations with New Zealand First.
"I actually think both parties have a position around an important focus on wanting to of course clean up our waterways. But there are things I just want to leave to having a conversation in private rather than in the public domain around those negotiations."
Ardern said both Labour and National had the right to talk to Peters about forming a Government.
"There's no question here that there is an argument for both blocks of parties to be having conversations...I absolutely acknowledge that Bill English as a major party took a larger portion of votes. However, at the same time New Zealanders voted against the status quo."
As to who was in the "box seat" for negotiations, Ardern said she wasn't able to judge that herself. Labour's chief of staff has contacted New Zealand First about setting up a meeting but nothing has been booked into the diary yet.
New Zealand First will hold a caucus meeting tomorrow.
Labour and the Greens are relying on the special votes to deliver them more seats so a Labour-Green-NZ First coalition would have more than a slim one-majority of 61. The results of those special votes will not be known until October 7.
By now National has identified all the NZ First policies it has in common with the party, those that clash with it, and those on which it's neutral. Labour is likely to be doing the same.
