France, March 1 -- In the centre of Nairobi, where corrugated iron roofs shimmer under the afternoon sun and narrow footpaths weave through tightly packed homes, lives 23-year-old Sharon Achieng. Although there was a time when she thought she'd merely survive, rather than live.

She grew up in Kibera, one of the biggest slum towns on the African continent. Her mother sold vegetables by the roadside, while her father drifted in and out of casual jobs.

Sharon loved school - the order of writing in notebooks and the certainty of exams - but when she became pregnant at the age of 16, all that changed. Her classmates whispered, and teachers avoided making eye contact with her. Eventually, she stopped going to school.

"I felt like the world h...