Morena was born María Cristina De Giacomi in Buenos Aires, Argentina. She is the youngest of four siblings and grew up in Palermo, Buenos Aires neighborhood with her upper-class family. Her father was an engineer and her mother was a sociologist. She studied at a traditional private religious school. When she was 17, she started working as a fashion model and became the popular face for Lee Jeans in the country. While she was modeling, she also studied social assistance in university and militated alongside Padre Carlos Mugica during the dictatorship in Argentina.