In 1975, Conceição joined the newly established "Organização Popular de Mulheres Timorense" (Popular Organisation of East Timorese Women) (OPMT), the women's organization of FRETILIN. At the time of the Indonesian invasion of East Timor in December 1975, she fled to the mountains. Here Conceição began teaching women who did not have the opportunity to study. This included reading and writing as well as sewing and embroidery. Conceição became leader of OPMT in Suco Bahatata, a village in the Uatucarbau Subdistrict. From 1976 to 1986 Lalo Imin, as she was called at that time, took part in the guerrilla struggle against the occupiers. In 1976 she was appointed Assistant to Zone 1912 in Baguia, and from 1977 to 1978 she was a commissariat delegate for the Eastern sector. Her husband Kilik Wai Gae was at the time commander of the Second Sector. In 1978 Conceição, with Xanana Gusmão, was a member of the group that built the resistance network in Lospalos.