Isabel Peron, now 75, had no comment as she was driven on Friday from her villa in the wealthy Villanueva de la Canada neighborhood to Spain's National Court, where Judge Juan del Olmo was considering the request to summon her to Argentina for questioning.
Peron was later granted conditional release while a decision is taken on whether or not to extradite her.
Maria Estela Martinez de Peron, known as Isabel, has lived in exile in Spain since 1981.
She assumed office after the death of her husband, Juan Domingo Peron.
Prosecutors claim Peron signed three decrees that cleared the way for acts of state terrorism during her rule between 1974 and 1976. She was ousted by a military coup in March 1976.
Many human rights activists say the dirty war really began with Peron and her once-powerful inner circle, whose October 1975 decrees called on the armed forces to "annihilate" people deemed to be "subversive elements".
Testifying as a witness in a 1997 Spanish case, Peron said she recalled approving the decrees but did not remember details and was unaware of any abuses during her presidency.
While Argentina's justice system has documented thousands of cases of human rights abuses committed under the 1976-1983 dictatorship, investigative judges have generally avoided looking into atrocities that occurred before the military coup.
Acosta reflected this new initiative when he signaled that not even the former president was untouchable in a newspaper interview: "I don't care one bit who she is. For me, she's just one more citizen."
Adolfo Perez Esquivel, who won the 1980 Nobel Peace laureate for his human rights work, told The Associated Press he believed the Triple A was effectively part of a state structure and thus the beginnings of state-backed terror.
He said: "Once and for all, we have to get to the bottom of this problem and find out how this terrorism was generated by the state.
"The search for the truth must go in every direction."
According to government figures, more than 11,000 people were killed during military rule, but human rights groups put the death toll at 30,000.
In Argentina, families of the victims celebrated the arrest including Maria Adela Antokoletz, whose brother was kidnapped shortly after the coup because he was a lawyer who defended leftists.
She said: "I believe state terror began before the coup. Those who signed these decrees knew perfectly well the nature of the campaign and what this repression would involve."
Peron's defenders say she could not possibly have anticipated the killings of hundreds of leftists and unionists her administration set in motion, let alone the military coup that expanded the terror to a full-scale dirty war.
Nestor Kirchner, the Argentine president who as a leftist lawyer was detained twice during Peron's presidency, backed the Supreme Court's decision to scrap amnesty laws in 2005 and has been outspoken since then in demanding full accounting for dirty war crimes.
He told an Argentine newspaper: "We want reconciliation, but with truth and without impunity.
"That's why we need to know the truth.
"If the judges believe there was state terrorism before the 1976 military coup, then those responsible need to be tried."