“This European parliament is probably going to be the most rightwing ever – and it will want to rip up the Green Deal,” said Lena Schilling, a 23-year-old climate activist turned Green politician, as she canvassed voters in a bougie market in central Vienna.

But even in this Green stronghold, shoppers seemed less interested in threats to democracy and climate policy than the candidate herself. A media storm has for weeks raged around Schilling on the back of newspaper reports that she spread harmful rumours – and the party’s response has thrown it deeper into turmoil right before voters head to the ballot box.

“The way the Greens have acted in the last weeks has been very hypocritical – attacking other parties and playing the victim,” said Diane, a German living in Innsbruck, a few metres from a vandalised campaign poster of Schilling’s face. “It’s the reason I’m voting for the [centre-left] instead of the Greens.”

Polls suggest Europe’s Green parties could lose up to one-third of their seats this weekend as voters drift to the right – a shift that could cap the continent’s green ambitions and unravel world-leading climate policies. In contrast to the elections five years ago, when school strikers such as Schilling and Greta Thunberg pushed climate up the political agenda, inflation and war weigh more heavily on voters’ minds.

In Austria, where the Greens are part of the national government, the party has also been hit by a scandal around its lead candidate that has led to public trust in her plummetting. The daily broadsheet Der Standard reported in May that Schilling had spread damaging rumours about several people, and published private texts in which she sharply criticised the Greens weeks before announcing her candidacy. She is being taken to court by one of the couples caught up in the story – a former friend and her husband who made her sign a document forbidding her from repeating the claims.

For a public struggling to make sense of the scandals, which have gripped this rich country of 9 million people, there is enough uncertainty around some of the allegations to fuel fiery debate. The Austrian press council has opened an investigation into the newspaper’s reporting that will explore its reliance on anonymous sources.

On a drizzly Saturday morning at a Greens’ bicycle turned campaign stand, passing shoppers see a double standard in media coverage that has subjected Schilling to more scrutiny than the lead candidates of other big parties, all of whom are men.

“I have to say, I see a sexist and voyeuristic component to this,” said Mariella, who leads the equality team at a local technical school. “It’s reached a point where there’s no longer any relevance for political reporting.”

Veronika, who works in the art scene, said she may vote for the Greens “in solidarity” despite not belonging to their political camp. “I’ve lived in Austria 20 years and have seen a lot of hate against young women – but never on this scale and in this form.”

But the criticisms have advanced far beyond Schilling herself. The Green party’s response to the crisis has added fuel to the fire that, for some voters, eclipses the original allegations.

When Der Standard published its report, the Austrian vice-chancellor, Werner Kogler, a senior Green, dismissed the allegations as “anonymous mumbles and farts”. The party’s secretary-general, Olga Voglauer, accused critics of using “Silberstein methods”, a reference to an Israeli political strategist who used dirty campaign tricks in the 2017 Austrian election: a charge that carries antisemitic connotations. Schilling’s reluctance to openly clarify the facts of the matter, which she says would involve sharing things about others she does not have the right to share, has cemented scepticism about her conduct.

The way the Greens have handled this is “simply inappropriate,” said Marie, a retiree who used to work for a government agency, adding that as a longtime Green voter she was unsure which party deserved her vote.

Appearing confident in TV debates and authentic on Instagram reels, Schilling belongs to a generation of activists who took to the streets every Friday and made the climate a priority for voters leading up to the European elections in 2019. Analysts say it gave a boost to parties promising strong climate action and helped secure cross-party support for the European Green Deal.

But after pandemic lockdowns pushed protests online and a series of crises turned public attention away from the environment, activists have increasingly asked themselves how they can best effect change. Some have turned to more radical forms of protest, while a handful have thrown their hats into the political arena.

From the Green party office in central Vienna, Schilling said her turning point came when she led a campaign to block a motorway expansion through a nature reserve – and won. Leonore Gewessler, the Green’s climate and transport minister, put the project on hold despite opposition from the party’s coalition partners, the centre-right ÖVP.

“It needed the protest, but above all it also needed the brave decision from somebody in a position of power,” said Schilling. “Since then I kept asking myself how I can best fight for the climate, for the future, for justice.”

But the decision also alienated activist friends from other parties, she said. “This candidacy has of course annoyed people,” said Schilling. “But I had not expected it to go so far that private chat messages would be published, instrumentalised and put in a false context.”

Young activists have often clashed with traditional Green parties over issues from nuclear power to social justice causes, and have criticised them for compromises made when in government. Gewessler, a fierce supporter of a proposed EU law to restore nature, is expected to abstain in a crucial vote this month unless Austria’s federal states lift a blockade against the policy.

Schilling said she has not had to put away causes close to her heart since entering politics. “At first I was almost a bit cautious about how radical I was allowed to be,” she said. “But it became clear relatively quickly that I can call for a ban on private jets – which I do.”