Pato had joined the Portuguese Communist Party in 1962, having waited some time to be accepted as a member, because of the need to prove her loyalty to the party. Returning to Portugal after her husband's death, she was part of the early efforts to establish the National Commission for Relief for Political Prisoners (Comissão Nacional de Socorro aos Presos Políticos - CNSPP), together with Maria Eugénia Varela Gomes, Aida Paula and others. They collected money for the prisoners and organised petitions for their release. She, herself, was arrested in June 1967 by the PIDE which had intercepted a phone call from another communist party member asking for her help to dispose of a suitcase full of explosives. She had already been under investigation for her involvement in the creation of the Movimento Democrático de Mulheres (Women's Democratic Movement). Pato was held in isolation at Caxias prison near Lisbon and was subjected to sleep torture. She was released in November of the same year. Eight days after being released, the River Tagus flooded north of Lisbon, killing 700 people. Pato joined the rescue mission.
