Piteira Santos began activities in opposition to the
Estado Novo dictatorship in 1934. She was an early member of the
Associação Feminina Portuguesa para a Paz (Portuguese Women's Association for Peace - AFPP), with her knowledge of German proving very useful during
World War II, when she assisted German Jewish refugees in Lisbon. She also joined her husband and other members of the
Portuguese Communist Party (PCP) in May 1938 in organizing the escape of the communist leader
Francisco Paula Oliveira, known as Pável, from the
Aljube prison hospital in Lisbon, where he had been very ill. Oliveira then lived in hiding with the Fiadeiro family before making his way to Paris and eventually moving to Mexico. Her son, António, was born in 1938 and was named after Francisco Paula Oliveira, who also went by the pseudonym of António Bugio. His
godfather was the future leader of the Communist Party,
Álvaro Cunhal. Around the same time, she joined the
Conselho Nacional das Mulheres Portuguesas (National Council of Portuguese Women - CNMP), led by
Maria Lamas. After the war, she obtained several jobs with German companies in Lisbon. Her daughter, Maria Antónia Fiadeiro, was a goddaughter of
Fernando Piteira Santos, another PCP member who would become the girl's stepfather when Stella married him in 1948, following her divorce from Fiadeiro. They endured long periods of separation because Piteira Santos was always in hiding from the secret police. Originally an active Communist Party member, he was to fall out with the Party, being expelled as a "traitor" for his views on the democratization of the PCP. Inevitably, criticism also fell on his wife. ==Arrest and Exile==