Casco began her career teaching civics and French at the College La Providencia and Normal School #3. She also taught at the Lyceum San Carlos. In 1940, Casco married Mariano Luís Lara Castro, who had been a soldier in the Chaco Wars, a lawyer and professor at the Catholic University of Asunción. Lara's father was Ramón Lara Castro, a journalist, president of the Paraguayan Institute of Historical Investigations and at one time served as the country's Minister of Foreign Affairs in Brazil. That same year, her uncle Estigarribia, who at the time was President of Paraguay was killed in an airplane crash, throwing the country into chaos. Both Casco and her husband adhered to the Liberal Party, even after it was banned by Estigarribia's successor, Higinio Morínigo. Morínigo, the only candidate on the 1943 ballot, ruled as an authoritarian president through persecution and banishment. Opposition resulted in the Paraguayan Civil War. When it ended in 1947, Casco became involved with helping political prisoners, as almost all of her maternal family had been exiled to Argentina and her paternal family lost all their property in Asunción. Her husband was also forced into exile, living briefly in Argentina and Uruguay, before his return to Paraguay in October 1947. Casco did not accompany him, as she was near the end of her third pregnancy and remained in Asunción alone with her sons Luis (born 1942) and Jorge (born 1945). Fernando (born 1948), was born soon after the Civil War ended and was followed by three more sons: José (born 1953), Fermín (born 1956), and Martín (born 1960). After both the Chaco War and the Civil War, her family lost their property and were sent into exile, leading Casco to become involved in human rights.