Kiwis were enjoying a complacent summer, there hadn't been a community case since November.
It was all going to change, in ways she could not have foreseen.
As RNZ's timeline shows, the first community case of the year was detected on 24 January, a woman who had travelled extensively in Northland.
That was followed by outbreaks in Auckland, clusters which were vigorously traced, ring-fenced and isolated.
Auckland was put into a level 3 lockdown, and then in March went down to level 2. The outbreaks were serious enough for Australia to suspend quarantine-free entry for New Zealanders.
Despite this, the first full year of Labour's majority government began well. The elimination strategy was working, the team of five million understood it and most of them supported it.
Managed isolation facilities were taking in infected travellers, nearly all of them returning citizens or residents.
Supplies of the Pfizer vaccine, reported internationally to be one of the most effective against Covid-19, had been secured although delivery was going to be spread across the coming months.
Covid-19 Response Minister Chris Hipkins said mass vaccinations should start mid-year.
Frontline workers and older people were vaccinated first but opposition parties began criticising the slow rollout for the general population.
Ardern and her ministers insisted there was no great rush, the country was learning from others and, unlike others, was not ravaged by the virus so did not need the vaccine as badly.
In April the quarantine-free bubble with Australia opened but it was paused the following month because of outbreaks across the Tasman. It popped in July, and was never reinflated.
Mass vaccinations began in late July but the take up was slow and opposition pressure mounted. There was still did not seem to be any sense of alarm in the community.
There was relentless criticism of the way the Maori rollout was being handled. They were lagging behind the rest of the population.
In her end-of-year interview with RNZ Ardern accepted the government could have done more to assist community-led vaccination efforts but defended the decision not to prioritise all younger Māori.
In August everything changed. The first case of the Delta variant arrived in the community, linked to a returnee from Australia. Somehow, it had escaped from the Crowne Plaza MIQ facility.
Ardern ordered a level 4 lockdown for Auckland and the Coromandel lasting four days, and three days for the rest of the country.
It didn't contain Delta, something no other country had been able to achieve, and cases spread in Auckland and to other centres.
Complacency had now been completely dispelled and there were queues at testing stations and vaccination centres.
Parliament was suspended as the vaccination rollout came under even more intense scrutiny.
National suspected the government had been slow to order the vaccine, something Hipkins denied, but there was no denying other developed countries had started much earlier.
The elimination strategy was becoming untenable, it wasn't working because Delta was too easily transmitted.
The government was reluctant to give it up. The strategy had delivered a huge election victory, but it didn't have a choice.
In subtle ways, the messaging began to change. "Zero tolerance doesn't mean zero cases" was creeping in, and in October, Ardern changed the game: "It's clear that long periods of heavy restriction has not got us to zero cases," she said.
There was still no admission that elimination had been scrapped.
Judith Collins, then National's leader, called on Ardern to "tell the truth ... the elimination strategy is clearly dead".
The government then began introducing steps within the alert levels, trying to relieve the pressure on Auckland which by then had been in various states of lockdown for months.
There were reports of confusion, the rules weren't clearly understood.
On 22 October the government revealed what was going to replace it - although it still said the aim would be to stamp out the virus where it appeared in small clusters.
The traffic light system was explained to the country. Lockdowns would be replaced by red, orange and green settings with red the most restrictive.
It would start when all the 20 DHBs had reached 90 percent full vaccination rates, a highly ambitious target. Ardern and Hipkins were careful to say the decision on when to switch the traffic lights on would be a "pragmatic" one.
That turned out to mean before all the DHBs had reached the target, most were still some way off.
The Auckland business sector was putting huge pressure on the government to end lockdowns and give it some certainty about the future
It did that on 29 November, announcing the new system would start on 3 December. Auckland and several regions with low vaccination rates would start at red, the rest of the country at orange.
Two weeks later it was announced Auckland and the other red regions, with the exception of Northland, would move to orange on 31 December, just in time for New Year. Businesses fumed over the delay but it appeared to be generally well received.
Cases of the Delta variant had increased to daily numbers which would once have caused immediate lockdowns, but were now barely noticed. Hospitalisation rates were steady and only a handful of people were in ICU.
Around mid-December Auckland cases began to decline - the vaccine was working and the city had rates above 90 percent.
Ardern told RNZ: "It was the year of the vaccine and to finish with rates in the mid-90 percent mark for first dose, 85 percent for Maori, over 90 percent for Pacific, I'm really proud of what New Zealand's doing."
She was right to be proud, what had been achieved during the year had been remarkable. In her last speech in Parliament before the adjournment Ardern said New Zealand had been through two years of Covid-19 and 44 people had died - minuscule when compared internationally.