Last week Pradenas, along with six other Chileans living in Madrid, took Britain to the European Court of Human Rights in Strasbourg in protest at what she considers an arbitrary decision by the House of Lords to airbrush her ordeal from General Pinochet's record.
The Law Lords ruled in March that only crimes attributed to the former dictator after September 1988 - the date that Britain signed the International Convention on Torture - would be considered as part of Spain's extradition request being heard this week by Bow Street magistrates in London.
"How is it possible that the kidnapping and torture inflicted on me was not a punishable crime, but would have been had it happened three years later?" she asks.
"The Lords' ruling guarantees Pinochet's impunity before 1988. We think the ruling incorrectly interprets the European Convention on Human Rights, which is supposed to favour the victim of human rights crimes and guarantees the non-impunity of the author of a grave human rights violation."
Marcela's case is not being considered this week, because it occurred before 1988, and her complaint against Britain will not affect the extradition hearings. But she insists that her ability to seek justice for the abuse she suffered has been drastically set back by the Lords' ruling.
"The Lords' decision felt like closing the door on my defence," she says. "It sets a dangerous precedent by suggesting that crimes of torture are unpunishable if they occur before a certain date. We want to tell the Lords that they have left us victims defenceless. I have Spanish nationality, so I am as entitled as any European to the protection of the human rights convention."
As a bright 18-year-old from a working-class family, Pradenas was fortunate to win a place to study law at the University of Chile in Santiago in 1985. Unlike most of her fellow students, she lived in a working-class neighbourhood where she worked with Catholic human rights groups. In the course of that year she was assaulted on three occasions by hooded assailants who broke her arms, sexually abused her and burned her with an electric iron.
"In June 1985, I was seized in the street by men who took me to a park, laid me across a bench and broke both my arms. Then they let me go. In July, I was attacked as I was leaving the university with my arms still in plaster and taken to a torture centre which police think was the headquarters of the National Information Centre, formerly the Dina security forces. They tortured and sexually abused me for several days, then threw me from a moving car at a wall near the national stadium."
Pradenas moved to a safe house belonging to the Vicariate of Solidarity, a Catholic human rights organisation. She had denounced the first attack to the police and, astonishingly, was offered police protection, so in September 1985 she returned to her parents' house, where the third attack occurred.
"My mother had popped out to the shops and I was alone, and the policemen on the door had gone for a coffee or something. Hooded men broke into the house. They hit me and burned me with an electric iron on my breasts, face and back. I passed out several times and they revived me by ducking my head in water. When neighbours came banging on the door they fled."
In February 1986, Pradenas came to Spain, and within months was granted political asylum. Later she obtained Spanish nationality, open to any Chilean legally resident for two years.
Why was it necessary to terrorise a young woman who barely remembered the coup 12 years earlier? "I was no one in particular. I was never linked to any political party, but active in human rights organisations. I was one of very few who complained about being attacked. I think they wanted to use me as an example, a warning to others."
The fierce repression that followed the 1973 coup had, by 1985, given way to a selective crackdown, she says, that nonetheless affected wide sectors of the population, such as the Catholic church and youth groups. "They chose their victims carefully. Hundreds of people were kidnapped and tortured in those later years."
After she settled in Spain, Chilean courts shelved her case because of lack of proof of who had tortured and kidnapped her, but they accepted that she had been kidnapped and tortured. "That was a big advance."
The complaint she submitted to the European Human Rights Court states that the Lords' ruling grants impunity to Pinochet's conduct before 1988, and "violates the principle that any internal legal ruling must be interpreted in the sense most favourable to the Human Rights convention... that guarantees the non-impunity of the author or agent of a grave human rights violation."
Marcela Pradenas was pregnant during that last attack. Her daughter, Marcela Paz, is now a lovely 13-year-old. "She was fine, luckily, but how can I forget the crime that was done to me?"Reuse content