She had more vacancies than most prime ministers because New Zealand First is no longer there andshe had not replaced two of her own last term.
More room for appointments means more room for bold moves.
The two biggest surprises were her appointment of Nanaia Mahuta as Foreign Affairs Minister, and Ardern's own willingness to demote her most poorly performing ministers, Jenny Salesa and Phil Twyford.
Foreign Affairs is always a prestigious role. The two most obvious contenders for Foreign Affairs were former Trade Minister David Parker and Andrew Little, a former Labour leader who is well versed in foreign affairs.
But Ardern had other plans for them in portfolios with very big workloads, Health for Little and Parker in his current Environment portfolio overseeing huge reforms of the Resource Management Act.
Nanaia Mahuta is untested in the role but as she showed in her first outing straight after the announcement, she is an experienced and careful minister. She has shown an aptitude through the water reforms in building strong relationships. And she is not likely to overshadow Ardern, who is ultimately responsible for foreign affairs.
Peeni Henare, the grandson of former Māori Battalion great Sir James Henare, is the new Defence Minister.
Having Māori in both Foreign Affairs and Defence is not new - Winston Peters and Ron Mark – held the portfolios last term.
But it makes a statement that Māori ministers will be up for all jobs, including the ones that represent New Zealand internationally, not just those that address social disparities.
Ardern was bold in her demotion of Salesa.
Salesa, the former Minister of Building and Construction, did not have a monumental failure as a minister in the last term in the way that Phil Twyford had as minister in charge of Kiwibuild.
But she was managed very carefully in order to avoid that happening.
And if you are a minister under constant watch, you are using up resources that could be used elsewhere.
Twyford was lucky not to have been demoted as a minister altogether but he has survived, possibly because of his history with the party.
He has been demoted from No 5 in Cabinet to No 23 outside Cabinet, to last chance saloon.
He lost Housing last term and now lost his beloved Transport portfolio. He has given the job that is never sought after – Associate Immigration. That is the person who reads all the immigration cases and decides which ones have merit and which don't.
Ardern has delicately balanced the representation of Māori and Pacific Island MPs in the Cabinet. It is an area that is not talked about publicly but it rankled with the Māori caucus last term that by the end, there were more Pacific ministers in Cabinet than Māori.
There are now fewer PI ministers but Poto Williams, of Cook Island descent, has had a huge jump in rankings from last ranked outside Cabinet to No 10 in Cabinet.
The biggest risk for the Cabinet is in the Health portfolio – the most important portfolio in a global pandemic.
This is the area in which Ardern has settled for compromise.
Possibly only four people could have done, Chris Hipkins, Megan Woods, Little and Parker.
The best thing for New Zealand may have been to insist that the incredibly able Hipkins continue with it and take over the whole Covid-19 response, and leave Education to someone else.
But she has effectively split Health between two senior ministers, Hipkins for Covid-response issues including testing by health officials, and Little for non-Covid response issues.