As a young girl in the placid Dutch countryside, Tanja Nijmeijer dreamed of a life of chastity, poverty and obedience as a nun. Instead, she took up an AK-47 in faraway Colombia, joined the country's largest and most violent guerrilla group, and has spent the past decade dodging air raids, planting explosives and enduring days-long marches through jungles and mountains.

Nijmeijer – who in the ranks of the Revolutionary Armed Forces of Colombia (the Farc) goes by the nom de guerre Alexandra Nariño – is part of the rebel delegation engaged in peace talks in Havana with Colombian government negotiators to try to end a 50-year conflict that has left tens of thousands dead and one tenth of the population internally displaced.

In an interview for the Guardian at the mansion she shares with 29 others from the Farc delegation in El Laguito, an exclusive suburb of Havana, Nijmeijer tries to play down the sudden celebrity she has become, given the oddity of her origins. "I'm not a star," she says. "I'm just another guerrilla fighter."

But her background has little in common with the roughly 9,000 other fighters in the Farc, most of whom were recruited from the poor peasant families of Colombia's remote countryside.

Nijmeijer was born in the Dutch town of Denekamp, near the German border, into a comfortable middle-class life. "When I was little I dreamed of becoming a nun, because I was raised in a very Catholic family," she says. "Then when I started school I began having serious doubts about religion and the existence of God. In university, I became a diehard atheist."

In 1998 looking for internship opportunities and adventure, she answered an ad in her college newspaper to teach English at a private school in the Colombian city of Pereira.

Before coming to Colombia, Nijmeijer says she "didn't know anything" about the Farc or the conflict that was at its height, with the guerrillas staging mass kidnappings throughout the country, overrunning military bases and sabotaging the infrastructure, while rival rightwing paramilitary groups massacred civilians.

She remembers that when she went to the Colombian consulate for her visa an official asked her: "Miss, are you aware that there is a war going on in our country?"

On her arrival in Colombia she grew aware of the country's vast social inequalities – by some counts 52% of arable land is owned by 1.5% of landowners – and about the Farc, whose purported aim is to fight for social justice.

After her internship she went home to the Netherlands but by 2002 she had returned to the country. By that time a previous round of peace talks between the government and the Farc had broken off and Álvaro Uribe, who was then president, was pushing a new hardline security policy.

Nijmeijer became involved in the Farc's network of urban guerrillas in Bogotá, helping to bomb police stations and the city's bus network, crimes for which she has been indicted in Colombian courts. Then she was called to join the ranks with uniform and rifle in hand. Her training, involving marches lasting days through thick jungle, nearly broke her, but her tenacity and revolutionary zeal impressed the commanders.

More than a decade later Nijmeijer only has a hint of an accent in Spanish and uses the colloquialisms and turns of phrases of Colombian peasants. She is unapologetic about her life choice.

"I am part of an armed movement and arms kill. No one denies that," she says. "The hardest thing for me in the guerrillas is the death of my comrades."

Nijmeijer was present when the Farc's top military commander, Jorge Briceño, alias Mono Jojoy, was killed in an air raid on his camp.

Recalling the moment in 2010, she says: "I heard the thump of the helicopter and then there were so many bombs falling that I said: 'No! This is where it ends'. After the first bombs we heard Mono cry out … 'Get the people out of here!' Those were his last words."

She says another difficult part of her guerrilla life has been separation from her family. Contact has been sporadic. In 2005 her mother was allowed to meet her in a rebel camp after traversing the country by helicopter calling out her daughter's name by loudspeaker. Nijmeijer will not say whether her family have seen her in Havana.

Though certainly the most media savvy, Nijmeijer says she is not the only foreigner in the Farc and that she has met Ecuadorans, Venezuelans, Brazilians and other Europeans.

"My case is not unique. This is a historic moment when capitalism, multinationals, and the economy are globalising, and struggles are also globalising, too."

Nijmeijer's presence in the Farc was first detected when the military found her journal at an abandoned camp after a bombing raid in 2007. The battered exercise book revealed the Dutchwoman's revolutionary passions, home sickness – and her apparent doubts about joining.

If the Farc managed to reach power would "the girlfriends of the comrades [be seen]) in Ferrari Testarossas with breast implants and eating caviar?" she wrote.

In 2003 Nijmeijer was chosen to act as translator for three American defence department contractors who were taken hostage after their plane was shot down over Farc territory.

She remembers one of the men, Marc Gonsalves, said to her: "If the government of my country wants it can come in here and wipe you all out in six months." To which she says she responded saying that if they were attacked they would all die, including the Americans.

Gonsalves, who was rescued by the Colombian army in 2008, later told the Miami Herald that he felt very threatened by the Dutchwoman, whom he dubbed a "real deal terrorist".

Nijmeijer says that despite the tough talk she felt a certain compassion for the hostages. "If for me, who was there of my own will, the life [in the jungle] was difficult, how hard it must have been for them who had not chosen that life."

In addition to the criminal charges she faces in Colombia, she has been indicted in the US for participating in the Americans' kidnapping.

The Farc is accused of indiscriminate killing of civilians, forced recruitment and kidnapping. She is unapologetic, saying the guerrillas are not the victimisers. "We have been the victims of this war," she says, despite the tens of thousands of civilians affected by Farc actions.

Notwithstanding the hardships of rebel life, after a month in the Cuban capital Nijmeijer says she "misses the jungle and the comrades".

What would her role be in a post-conflict Colombia? "I am a Farc guerrilla and will continue to be one," she says. "If we achieve peace with social justice I would stay in the Farc and continue to do what is needed."

Peace talks

Delegates for the government of Colombia and Farc rebels are locked in negotiations to try to end the country's war, with both sides saying that the talks, which are being held under a veil of secrecy, are going well.

Seuxis Paucias Hernández, a Farc member, known as Jesús Santrich, told reporters in December that the two sides were engaged in a "respectful discussion" in which they are putting forth their positions.

Colombia's president, Juan Manuel Santos, has said that while the pace of the talks has been positive, Colombians should "have patience and not demand immediate results" because negotiators were dealing with "some very complex issues".

A Gallup poll last month showed that while 71% of Colombians supported the peace process, only 43% believed they would end in a peace deal.

The negotiations started off with discussion on land access and agrarian reform, often cited as one of the core issues in Colombia's armed conflict. A national forum has come up with 400 proposals.

Four other issues on the agenda are illegal drugs, political participation, disarmament and reparations for victims.

Agencies