In her offices on the top floor of Denmark's Parliament, stuck in the middle of the difficult party negotiations over the new Government, it's clear that she has moved a long way from her activist beginnings.
But she dismisses the focus on her as a person as an attempt to explain away the success of her party.
"The pundits are in shock. They think, 'oh, the Socialist party has grown so much', and then they say, 'oh, the people, they don't really agree with the policies, they just voted for Johanne because she's young and beautiful'."
This is exactly the line taken by Michael Ulveman, press secretary for the former Prime Minister, Anders Fogh Rasmussen, who believes Schmidt-Nielsen's popularity will be short-lived: "I think the population is going to have a wake-up call, because they don't have many figures like her.
"There will be a lot of members of Parliament now who have very extreme left wing opinions."
Schmidt-Nielsen scoffs at this: "The right wing have been trying to mount this scare campaign against us, saying 'Johanne is really a dangerous communist and she will make us like North Korea or Albania'. But it didn't really work. It's difficult for people to blame me for the Soviet Union. I was born in 1984."
Schmidt-Nielsen is skilled at using her youth like this, to deflect criticism or make her opponents look out of touch. When, at 23, she fronted for her party in the 2007 televised election debates, Bendt Bendtsen, leader of the Conservative party, asked her for coffee, thinking she was a production assistant.
The story overshadowed everything else in the press afterwards. "I do not think they would do that now," she laughs.
Schmidt-Nielsen has been in politics for 15 years.
"I was 12 when I got involved. There were a lot of children at school whose parents didn't really have the ability to help them, and I thought, why's the school not helping them?"
This led to her becoming vice-president of the secondary school students association, standing as a Social Democrat. "But then, when I was 15, I thought, that's too right-wing for me," she says. So she joined the anti-globalisation movement, protesting in Prague, Gothenburg, Brussels and Rostock.
"I'm an anti-capitalist and a socialist, is that so radical? It's just so obvious that the climate can't deal with this way of producing goods. I don't believe that the task for the rich countries is to get more growth; it is to redistribute the wealth that we already have."
Top of her agenda is to undo the draconian migration laws that the far-right Danish People's party has pushed in during its backing of the Liberal-Conservative coalition.
She's also determined to block moves to limit unemployment benefits and raise the retirement age.
"For 10 years, there has been this logic that if you just keep whipping the unemployed, suddenly a lot of new workplaces will come up in Denmark like magic and it's not happening, of course, because the problem isn't that they don't want to work, the problem is that there's no place for them to work."
Schmidt-Nielsen also has more radical goals: she wants to nationalise the energy industry, set up a state-owned bank, impose a tax on the financial sector and withdraw from the EU.
But she refuses to offer grandiose solutions to Denmark's problems. "We know that we can't get everything that we want," she concedes, seeing her role as bringing the demands of the activist movement into Parliament.
But her agitprop days may be over. "Perhaps I'm not going to throw 200kg of pasta again," she says. "If you knew how much time it takes to make 200kg of pasta, it's hard work."
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