After she finished her studies, Castellanos became a professor at UNAH in 1978. She was head of the Social Sciences Department and President of the Association of Teachers from 1997 to 2001. Castellanos was also the President of the Association of Professors of the University Center of General Studies (CUEG) in 1986, Coordinator of the Violence Observatory since 2005, consultant to the Arias Foundation for Human Progress and the Washington Office on Latin America (WOLA), and Research Associate of the Centro de Documentatión de Honduras (CEDOH). For 13 years, Castellanos was also the author of a newspaper column.