But she is not. She is healthy, lives with both parents and enjoys going to school. Unlike many of her friends, she has no plans to get married or have a baby any time soon.
Half of girls in Mozambique are married before they turn 18 - nearly one in five before the age of 15. About 1.2 million school-age children were not in education in 2012, more than half of them girls.
"In my neighbourhood, it is normal for girls in their early teens to be having babies or abortions, and dropping out of school to care for their children," says Marcelino, pictured below. "It's not because they want to. Many are unaware or are deceived and abused by older people."
She decided to take a different route, and has been an outspoken children's advocate in her school. At the age of 10, she was elected into the Mozambican Children's Parliament, which is supported by Unicef, the world's leading children's organisation, where she has been active ever since.
When the Glasgow Commonwealth Games Queen's Baton arrived in Maputo last week, Marcelino was at the airport to welcome it, invited by Unicef and the ministry of education. In Mozambique, Unicef trains teachers, provides school materials, builds toilets that girls feel safe using, and helps integrate sports in the curriculum.
When the baton was formally handed over, Marcelino addressed the crowd. She said: "My dream is to study sports, to increase my knowledge and become an adult armed with education and a healthy life. Let no-one force girls to marry, get pregnant, or leave school, nor to subject them to abuse and violence."
The Herald and Sunday Herald Children of the Commonwealth series will run over the coming months as the Queen's Baton travels the world on its way to Scotland. We're raising money for Unicef, an official charity partner of the 2014 Commonwealth Games in Glasgow. To donate, call 0800 044 5777; click on www.unicef.org.uk/herald; or you can text 'CHILD' to 70111 to donate £3.