Quintal was born as Miquelina Maria Possante Sardinha in the municipality of Avis in the Portalegre District of Portugal, on 11 November 1902.

When she was a child, her parents moved to Ponte de Sôr in the same district, where her father joined a group of anarchists who shared his secular and libertarian views.

From an early age, Quintal met influential anarchist figures that the family received during conferences held in the region.

With the school being accused of using a teaching method contrary to that supported by the Catholic Church and the State, the municipality of Ponte de Sôr ordered its closure in 1924.

Her husband attended the founding conference of the Federación Anarquista Ibérica (Iberian Anarchist Federation), which took place in Valencia in Spain in 1927 but, on his return, was arrested and sent to a prison camp in Angola, where he was kept until 1929.