There’s no doubt Jacinda Ardern taking over as leader is the best thing that has happened to New Zealand Labour in a long time, with its polling surging by 19 points in just a month as the phenomenon dubbed “Jacindamania” grips the country. There are the T-shirts, the tote bags with her face plastered on them, the “Let’s do this” slogan, and the memes flying around social media – but underlying all this is a serious groundswell of support.

Ardern, 37, the youngest person to lead the party, has taken a crash course in leadership and passed, so far, with flying colours. Just seven and a half weeks out from the 23 September general election, Andrew Little resigned as Labour leader after its lowest ever poll result of just 24 points.

The party unanimously chose Ardern, who had previously said her sights were not set on the leadership. Hours later Ardern fronted the media for the first time in the role and was impressive – fielding questions effectively and surprising political pundits with her confident performance.

The memes starting flying. Paul Le Comte shared one of Ardern as The Bride, played by Uma Thurman in Quentin Tarantino’s film Kill Bill, wearing the iconic yellow onesie.

Labour also received nearly $500,000 in donations in the days after Ardern took charge. And 3,500 volunteers signed up.

Soon after there was “are-you-having-kids-gate” where Ardern was asked by cricketer turned breakfast host Mark Richardson if she planned on having children: “I think this is a legitimate question for New Zealand, because she would be the prime minister running this country – she has our best interests at heart, so we need to know. If you are the employer of a company you need to know that type of thing from the woman you are employing … the question is, is it OK for a PM to take maternity leave while in office?”

Ardern’s potent response to condescending questions about baby plans from a middle-aged male broadcaster made it to the Washington Post and National Public Radio in the US. She started, firmly and politely, by saying that she would answer those questions because she had opened herself up to them in her public role.

But then she wagged her finger at Richardson and unleashed fury: “For other women, it is totally unacceptable in 2017 to say that women should have to answer that question in the workplace.”

She was swiftly backed up by the Human Right Commission which – in a post that took off like a rocket on Facebook – pointed out it is against the law for employers to ask about pregnancy, contraception or family planning.

Ardern had confronted – and shattered – the same sort of sexist double-standard imposed on childless leaders like the former Australian prime minister, Julia Gillard, and the British prime minister, Theresa May. It galvanised women across New Zealand, getting them excited about politics again.

Soon afterwards, Ardern fired up the youth vote by announcing three years’ free tertiary education.

Within the first week of Ardern’s leadership she delivered a poll-quake: Labour jumped nine points in a week, from the party’s low 24% under previous leader Andrew Little. This week, Ardern’s Labour jumped to a 10-year high of 43 points, overtaking the National party by two points – a six-point jump from the last poll, for a whopping overall 19-point gain since she assumed the leadership.

Labour has risen, and risen, and risen again, in each poll since 30 July. Political commentator Bryce Edwards says the Jacinda effect – the explosion of interest and positive support she has brought to Labour – is unprecedented. He describes her as a rising star in politics – someone with the X-factor, transforming the party’s grey old look.

When asked how long Jacindamania might play out, Edwards replied: “Nine years? I don’t see it subsiding anytime soon. She’d got such huge momentum. And for those on the left, who have suffered being electorally unpopular for so long, she really is a hero.

“That [latest] poll really showed that she’s magic.”

Ardern may have an X-factor, but she has worked tirelessly to ensure there is gravitas to back it up. Things have come a long way since an infamous exchange in 2012, when Ardern was debating head-to-head in parliament with then social development minister Paula Bennett. Bennett attempted to answer opposition questions, but was faded out by interjections. She shot at Ardern: “If you want to listen to the answer, zip it, sweetie.”

Five years on from that exchange, Ardern confidently slapped down Australia’s foreign minister, Julie Bishop, who said it would be “very difficult to build trust” with a Labour government in New Zealand. Bishop was commenting on Labour MP Chris Hipkins’s involvement in the citizenship saga surrounding Australia’s deputy prime minister, Barnaby Joyce, that has left Australia’s slim-majority conservative coalition government in a fragile position.

In her extraordinary outburst, Bishop accused New Zealand Labour of collaborating in a plot to destabilise the Australian government. Ardern’s response was sharp and decisive: she immediately registered her displeasure with the Australian High Commissioner, and rounded on Bishop. “It’s highly regrettable that the Australian foreign minister, Julie Bishop, has chosen to make false claims about the New Zealand Labour party. I have been utterly transparent about this situation,” Ardern said. “I stand by my statements this morning that I knew absolutely nothing about the Barnaby Joyce case until it broke in the media yesterday.”

Bishop and the Australian government were rewarded with ridicule; Ardern gained another chance to burnish her tough and politically accomplished image, at home and abroad. When it comes to building trust with a New Zealand Labour government, Bishop might have to think again.