She was taken to a hospital, issued a certificate confirming her virginity, and then taken to a hotel room where a she was raped for days. She was returned home after three nights.
Sephak grew up in Svay Pak, a poor fishing village on the outskirts of the Cambodian capital of Phnom Penh. It's a community that has become notorious as a place to buy child sex.
Her mother, Ann, said her family had fallen on hard times and that they took out a loan that eventually spiraled to about $6,000 in debt. With money-lenders threatening her, Ann took up an offer from a woman who approached her promising big money for her daughter's virginity.
Sephak said her mother was paid $800. But after Sephak's return, her mother began pressuring her to work in a brothel.
Ann said she regrets her decision and that if she had known then what she knows now, she would never have sold her daughter.
Return to the epicenter
The CNN Freedom Project first spoke with Sephak in 2013
, along with other child trafficking victims, as part of a documentary
on sex trafficking in Cambodia.
Sephak was rescued from her former life by anti-trafficking non-profit Agape International Missions
(AIM). Now a woman, she works alongside other survivors in a factory run by AIM, earning money making bracelets and clothing
"Today, I feel more much stability than before. Not a lot of stability, but enough," says Sephak. "Now I have a decent job. I really want other people to have the kind of work that I have."
American Don Brewster founded AIM in 2005 to fight child trafficking in Cambodia. A former pastor, he says the organization has so far rescued more than 700 people.
Most of his efforts are focused in Svay Pak. It's a place where the poverty is overwhelming, with many families scraping by on less than a dollar a day. The residents are mostly undocumented Vietnamese migrants, many of whom live in ramshackle houseboats on the Tonle Sap River, eking out a living farming fish.
"When we talk about child sex trafficking, this was at one point the epicenter," says Brewster.
"We would say when we came [to Svay Pak] it was 100% -- if you were a girl born here, you were going to be trafficked. We would say today it's significantly below 50%."
But Brewster has warned that although children are no longer being sold in brothels here, trafficking is now taking place in hotels, where it is harder to detect, and harder to prevent.
The US Department of State's 2017 Trafficking in Person's report
says Cambodia does not fully meet minimum standards for eliminating trafficking, but notes that the Cambodian government has made significant efforts to fight human trafficking, including increasing the number of trafficking convictions.
'Sometimes there's no choice'
As AIM's director of investigations, Eric Meldrum works alongside Cambodian police to track down criminals and rescue victims. He says that in three years, he has helped rescue 130 girls in more than 50 different raids and that AIM's partnership with police has been crucial.
"The police are doing a good job," he says. "We've got a very good cooperation with them and there's a definite willingness throughout the police, throughout the hierarchy of the police, to crack down on the issue."
Meldrum adds: "This is still a poor country and people are still looking to get money and unfortunately, with a lack of education, lack of jobs, the sex industry is one of the routes that people can make money to send home.
"Even sometimes families don't want their daughters or girls in the industry, sometimes there's no choice."
In spite of the efforts of NGOs and police, that's a reality still faced by many girls in Svay Pak.
"It's hard to understand why these mothers do this," says Sephak. "They don't have money, so they make their daughters work.
"Even now, I see a lot of mothers who don't understand the feelings of their daughters. They don't understand that their daughters have hearts, that they suffer."