Luana, known as Lulu, is believed to be the youngest to benefit from the country’s new Gender Identity Law, which was approved in May 2012.
The act enshrines the right to be identified by name and sex as defined by the individual.
As a result, the governor of Buenos Aires, Daniel Scioli, approved Lulu’s application to change her name from Manuel on her DNI, the Argentinian identity card, and birth certificate.
“The government of the province of Buenos Aires has decided to provide a solution to this particular case raised by the family,” Alberto Perez, chief of staff, said, according to La Nacion.
The decision was made after Lulu’s mother, Gabriela, wrote to Mr Scioli as well as Argentinian president Cristina Kirchner. She said her daughter identified herself as a girl as soon as she started talking.
“By accepting that my son was not the son I gave birth to, but a girl, I accepted her identity and put myself at her side,” said Gabriela, from Greater Buenos Aires.
Lulu, who has a twin brother, was refused the request last December because of her age.
But the Children, Youth and Family Secretary ruled children under 14 were capable of giving consent and cited international human rights in overturning the decision.
Argentinian reports suggested it was the first time anywhere in the world that a transgender child had been able to change their identity through an administrative process without resorting to the courts.
Alfredo Grande, one of the psychologists involved in the case, told Folha de Sao Paulo: “The DNI is like a mirror. If a person doesn’t identify themselves there, it’s not good.
“It was an important fight that we won.”
Cesar Cigliutti, head of Homosexual Community Argentina (CHA), which supported the family, said Lulu’s case was “historic”.
Mr Cigliutti told La Nacion there were “thousands and thousands” of Lulus in their 30s, 40s and 50s, whose parents had not allowed them to live according to their identity.
“They had a terrible life, of self-usurpation,” he said.