"I told them I never wanted to get married and I wasn't going back. I ran away because I wanted to stay in school," Susmita, now 16, said.
Although Nepal banned child marriages in 1963, four out of ten girls are married before they turn 18, according to Unicef.
The figures are even higher among the country's impoverished Dalits or "untouchables" who live in remote communities shunned by the mainstream.
Three out of four Dalits marry during their teenagers or earlier, according to a 2012 survey by Plan International, Save the Children and World Vision. Girls are often abducted by prospective grooms in a cultural practice few families object to.
Susmita was kidnapped and forcibly married four days later — an ordeal her own mother, Jadane Kami, endured when she was a teenager.
"This is our culture. People worry that otherwise our girls will elope or marry into other communities," said Kami, who initially did not oppose her daughter's forced marriage.
The tradition has survived a ten-year civil war, the end of royal rule and Nepal's transition to democratic politics.
In Simikot, Dalits live in segregated settlements.
Their hay-topped homes stand in stark contrast to the shiny tin roofs of houses belonging to higher-caste Hindus and Buddhists.
"Dalits have struggled due to their low caste status. For centuries, they were not allowed to mix with others at all," said deputy district chief of the remote Humla district, Bam Bahadur KC.
"Naturally, this has left them very isolated, they are still following old customs and change has been slow to come," he said.
Dalit families also labour under huge financial strain, with children pushed to leave school and start work while their parents eke out a living.
Dana Sunar, now 18, had been the last Dalit girl in her class. While others had dropped out, Sunar dreamed of becoming a schoolteacher.
But she was taken at 14 and forced to marry an 18-year-old farmer earning US$50 (Dh184) a month.
"I cried and cried. It was like a door had closed before me, any dreams I had were gone," Sunar said.
Her in-laws made her drop out of school and focus on farming and housework. Now a mother to six-month-old twins, Sunar describes her new life as "a daily struggle".
"We never have enough money — sometimes we eat only once a day. I don't know how I am going to bring up these children," she said.
Experts say the consequences of marrying so young are devastating and laws are ineffective. Susmita, now in ninth grade, said she wanted to see an end to "this terrible custom".
Her father, who earns $80 a month, said sending her to school was a struggle. But for now, her family will do whatever they can to keep her in class.
"I think she did the right thing by running away," her mother said. "She is more brave than me — I never felt like I had a choice in the matter."