Balkissa Chaibou dreamed of becoming a doctor, but when she was 12 she was shocked to learn she had been promised as a bride to her cousin. She decided to fight for her rights - even if that meant taking her own family to court.

"I came from school at around 18:00, and Mum called me," Balkissa Chaibou recalls.

"She pointed to a group of visitors and said of one of them, 'He is the one who will marry you.'

"I thought she was joking. And she told me, 'Go unbraid, and wash your hair.' That is when I realised she was serious."

The young girl from Niger had always been ambitious.

"When I was little, I was dreaming of becoming a doctor. Take care of people, wear the white coat. Help people," she says.

Marriage to her cousin, who had arrived with his father from neighbouring Nigeria, would make this impossible.

"They said if you marry him you won't be able to study any more. For me my passion is studying. I really like to study. That's when I realised that my relationship with him wouldn't work well."

Niger's tradition of marrying its girls young - it has the highest rate of child marriage in the world - is partly rooted in its grinding poverty.

"The dynamic works in this way: I have lots of children, and if I can marry off one child that is one child less that I have to feed," explains Monique Clesca, the United Nations Population Fund's representative in Niger.

Balkissa Chaibou's parents had five daughters, so from their perspective marrying her to her cousin may have made economic sense.

But another reason for the tradition of early marriage in Niger is the belief that it reduces the risk of pregnancy outside wedlock.

"Nowadays some children are not well brought up," says Hadiza Almahamoud, Chaibou's mother. "If they are not married off at an early age, they can bring shame to the family."

Chaibou continued to work hard at school, waking at 03:00 to study, but as she got older the looming marriage with her cousin became a distraction.

Read more: http://www.bbc.com/news/magazine-35464262

Balkissa Chaibou appears in the four-part documentary series Her Story: The Female Revolution which will air on BBC World on 20th February, 27th February, 5th March and 12th March. Find out more about the documentary.