The phone call gave her five days to mentally adjust to the possibility and after Little's kamikaze interview with TV1's Corin Dann in which he said he had thought about resigning, it became inevitable.
Little has been one of the few recent Labour leaders who was undermined by outside forces, not by his own caucus.
He was not actually a bad leader and his time in the leadership was not wasted.
It has contributed to him becoming a strong member of the Government, with responsibility for Justice, the spy agencies, Pike River re-entry, and Treaty of Waitangi negotiations.
Little is certainly one of the most visible members of the Government.
He combines a broad breadth of portfolios with a refreshing habit of saying what he thinks and an availability to the news media that often only the busiest and most organised of ministers can manage.
As leader, Little managed to discipline a divided caucus. He focused on what he could control. He learned how to manage conflicting advice and be decisive.
Less than two weeks after getting his ministerial warrant, he announced that Teina Pora's compensation for 20 years' wrongful imprisonment would be inflation adjusted.
The previous Government had been content to let Pora fight the unjust payment through the courts rather than making the obvious and only fair decision.
That experience as leader has given Little a confidence that many other new ministers don't have – but it also comes with dangers.
Little's confidence stretches into stubbornness, arrogance and even belligerency. He gets into scraps that other ministers would avoid and, as shown this week with the Australian Home Affairs Minister Peter Dutton, is more likely to fan the flames than calm things down.
Little's scrap with Australia over some of the least deserving detention or deportations of Kiwis will be doing Dutton's ambitions no harm at all with his domestic audience.
Ardern herself had a run-in with Dutton in the first month of her premiership over the housing of asylum seekers on Manus Island and Nauru.
The greater nervousness in Government is over Little's performance is in the criminal justice area where he is leading the effort to cut the prison population without being labelled 'soft on crime.'
Come the day that Dutton is leading the Liberals or possibly Australia, the run-ins with New Zealand could be more consequential but politically at present neither party is being damaged - quite the opposite.
The greater nervousness in Government is over Little's performance is in the criminal justice area where he is leading the effort to cut the prison population without being labelled "soft on crime."
The potential for miscalculation is vast and the damage to the Government enormous if Little strikes the wrong tone, picks the wrong fight and gets the public offside with the project, which opens with a summit next month.
He miscalculated badly in his bid to repeal the Three Strikes law by promising it before cabinet had approved it and before New Zealand First had committed to it.
He has not backed away from calling victims' campaigner Garth McVicar loopy.
He endorsed a bid by advisory group chairman Chester Borrows to get the media not to run emotive stories about victims and stick to evidence-based approaches to crime reporting.
That is about as realistic as politicians agreeing to keep emotive arguments out of an election campaign because it might affect the way people vote.
Little may be expecting to win hearts and minds through rational and reasoned argument but he is not so flash at adhering to it himself.
Ardern, who is likely to return to work from maternity leave in just over two weeks, may come back with fresh appraisals and advice for some of her ministers with the benefit of distance and Little should listen if she has any for him.
Whatever the ministerial fortunes of this term hold, Little has secured a place in Labour history as having made a personal sacrifice for the good of the party after concluding, possibly wrongly, that Labour could never be in Government with him as leader.
Just before Little resigned, Labour, the Greens and New Zealand First were on 50 per cent in the Colmar Brunton poll – and that had been a longstanding trend: the month before they had 49 per cent, 48 per cent, 49 per cent, 52 per cent and 49 per cent.
The votes were sloshing around among the three parties but in total, hardly moved in six months, even with Ardern.
The actual 2017 election result for the three parties combined was 50.4 per cent.
There is no mistaking that Ardern made a difference to Labour's polling and morale, and made the choice by New Zealand First easier.
But the view that New Zealand First would never have formed a Government with a Little-led Labour Party can only be conjecture.
Little is not one to waste time wondering about what-ifs. He has too much on his plate, but not so much that he couldn't put in a call to Jacinda Ardern on Thursday, simply to wish her happy birthday.
