The answer, of course, is that Ardern - just like Little before her - believes Labour will be marked down if it puts a pledge to introduce capital gains tax before voters at this month's election.
So what else will be on a Labour Government's agenda?
Ardern could rule out land taxes. She could rule out wealth taxes - like estate taxes, death duties and gift duties. But it is notable that only the family home has so far been declared sacrosanct.
Then there are other options. What happens to company and personal income taxes when a Labour Government needs to raise more revenue?
Ardern has ruled personal income tax hikes off the table. But for how long?
Grilled by the Herald's political editor Audrey Young in what was billed as a "job interview" for the prime ministership, Ardern went on to say it was her "captain's call" to not rule out introducing a capital gains tax on rental properties or second homes in Labour's first term as a Government.
During the election campaign, Ardern has repeatedly stressed that Labour will wait on recommendations from a proposed tax working group before finalising its options. She told the Herald that waiting to act until after the 2020 election was too long - stressing that any capital gains tax would not apply to the family home.
"It is different leadership, different decisions," Ardern told the Herald interviewing panel.
"Andrew [Little] made a call that he would go back to the electorate.
"I made a call that if I was in Government and presented with a tax working group paper that suggested these are the things you need to do to be able to tackle the housing crisis and inequality in your tax system, to then sit on that for one, maybe two years without doing anything didn't feel right to me."
Ardern said she had talked to finance spokesman Grant Robertson, but it was her "captain's call".
In fact, it is risible that any potential Prime Minister would be calling the shots in this matter, reducing her putative Finance Minister to a political eunuch.
Anyone who believes that Robertson is not in on the political ploy does not know him well.
He has held the finance role since November 2014, when Little reshuffled Labour's shadow Cabinet. His signature focus has been Labour's "Future of Work Commission", which has examined policies to address the impact of technological change on work and jobs.
The term "captain's call" hit the Australasian lexicon during former Liberal leader Tony Abbott's brief term as Prime Minister.
The Urban Dictionary is brutal, defining a captain's call as "a decision made unilaterally by a team leader without consulting colleagues, often a massive clusterxxxx".
This is not where PM Ardern wants to end up. More clarity, please.