She has for decades fearlessly criticized the government, speaking out against corruption and abuses, and notably getting under the skin of President Nicolas Maduro.

"You all see how she skips, jumps, shrieks," Maduro said in 2014 when he accused her of involvement in one of the many coup plots he has denounced against him.

"Because she is a woman people are going to say, 'Maduro attacks women'. I am not attacking her, I am merely mentioning her," because her name came up in the investigation, he said.

San Miguel, 57, was arrested last Friday in the immigration area of an airport in Caracas along with several family members who have since been freed on bail.

Prosecutors accuse her of "treason" and "terrorism" over her alleged involvement in a more recent plot the government claimed to have uncovered to assassinate Maduro.

Her ex-husband, a retired soldier, was also arrested and is being charged with allegedly revealing "political and military secrets."

International rights groups see in the arrests a coordinated plan to silence government critics and perceived opponents.

- Investigating the military -

San Miguel is the founder of an NGO called Citizen Control, which investigates security and military issues, such as the number of citizens killed or abused by security forces.

She has detailed military involvement in illegal mining operations, and a recent femicide in the army.

She started the organization two years after she was fired in 2003 from a state entity after she backed a call for a referendum to recall then-president Hugo Chavez from office.

San Miguel, who also has Spanish citizenship, is a lawyer specializing in rights and international law, but also has a masters in security and defense from the Institute of Higher Studies of National Defense, attached to the Venezuelan Armed Forces.

"She has participated in different legal actions precisely in favor of democracy and the defense of human rights," said Martha Tineo, coordinator of the JEP rights organization.

"Why is she being detained? We might think that attacking Rocio San Miguel is a way to attack all women human rights defenders in Venezuela."

- Standing up for journalists -

Venezuelan journalist Andreina Flores recounted to AFP a story of how San Miguel intervened when she and another reporter were detained by soldiers in 2016 -- a volatile year marked by economic crisis and protests against Maduro's government.

"Rocio arrived and was relentless with the soldiers, but always calm," said Flores, now based in Paris.

She reeled off "articles of military law, the constitution, requested copies of statements, the accusation."

The soldiers released them then and there, and the pair got into San Miguel's car and she drove off with them.

In 2018, San Miguel won a case against Venezuela at the Inter-American Court of Human Rights for the violation of political rights and freedom of expression over her 2003 dismissal from a state border agency.