Then two years ago, the letter came. She had been granted a scholarship to study law at a university in Durban. She had the chance few poor South Africans get — to flip her destiny.
Now, at 20, instead of studying in the university library and writing law assignments, this bright and perceptive woman spends her time dashing around a clothing factory floor as an errand girl in a blur of exhaustion, earning less than $10 a day to take home to her 14-month-old daughter.
"I look back and say, 'You gave up your life. You had it on a silver platter. You really put yourself in a situation where you have no future.'
"That night, I never gave myself the opportunity to think about the consequences. It really breaks me sometimes, that I am responsible, I did it on my own. I was really, really irresponsible to such a point that I look at my daughter and I see my degree."
But she hasn't lost hope for a better future. She called her child Thembeka, or Faith.
Tens of thousands of South African girls drop out of the education system annually because of pregnancy and most never return. In 2009, more than 45,000 schoolgirls became pregnant, including 109 third-graders, according to a report released two months ago by the Department of Basic Education.
The rate of pregnancies for teens 15 to 19 in South Africa in 2009 was 73 per 1,000, according to the report, one of the highest rates among developing countries (as South Africa, increasingly, is seen by humanitarian agencies). The rate compares with 26 per 1,000 in Britain and 41.5 in the U.S. The problem is even more acute here in eastern KwaZulu-Natal province, which has the highest rate of teen pregnancy in South Africa, leading to high dropout rates among girls.
That has serious implications for a country with high poverty and unemployment, a failing education system that has betrayed the aspirations of the post-apartheid generation, and a disastrous shortage of skilled people that threatens economic progress.
For each year a pregnant teen remains out of school, her chances of returning diminish sharply, experts say.
"Practically, they don't go back to school," said Farshid Meidany of the South African arm of Maryland-based aid organization Medical Care Development International. The organization runs projects in South Africa on HIV/AIDS, tuberculosis, child survival and maternal health, including one here in Mavela, outside Durban, for AIDS orphans, teen mothers and others.
"How can you go back? First of all, there's discrimination by teachers and colleagues," Meidany said. "And there's the work. They become premature adults."
Marx, as petite and poised as a ballerina, with huge, almond-shaped eyes, nurses her baby on her lap as she tells the story of her life with disarming self-perception.
She seems wise beyond her years, yet looks small and frail when she walks into the factory to a job she hates. When young men in the street call flirtatiously, she half-turns, half-smiles, then turns away from them, steels her expression and walks up to the factory gate.
Marx's childhood was so harsh, her chances of a better life were perhaps never very great. When her mother, a fair-skinned woman of mixed race, saw the baby for the first time, she was horrified that the darker-skinned child was obviously the progeny of an Indian client, not her boyfriend. She nearly left her at the hospital.
"She said I was such an ugly baby."