When Kieu was 12, her mother asked her to take a job. But not just any job. Kieu was first examined by a doctor, who issued her a "certificate of virginity." She was then delivered to a hotel, where a man raped her for two days.

In 2013, the Freedom Project went to Cambodia with Oscar-winning actress and UNODC Goodwill Ambassador against Human Trafficking, Mira Sorvino. The result was "Every Day in Cambodia: A CNN Freedom Project Documentary," which looked at child sex trafficking in the country.

In Svay Pak, a notorious child sex trafficking hub in Phnom Penh, Sorvino met Kieu, who was then around 14 years old. She had been rescued from sex trafficking by Agape International Missions (AIM), a non-profit for trafficked and at risk children and teenagers.

Kieu told of how she had been sold aged 12 by her mother to a Khmer man of "maybe more than 50" who had three children of his own, Sorvino explained in her Cambodia journal: "The price set in advance for her virginity: $1,500, though she was ultimately only given $1,000, of which she had to give $400 to the woman who brought her to the man. Her mother used the money to pay down a debt and for food for the fish they raise under their floating house -- their primary income source.

"Beforehand, Kieu said, 'I did not know what the job was and whether it was good for me. I had no idea what to expect. But now I know the job was not good for me.' After she lost her virginity to the man, she felt 'very heartbroken.' Her mother supposedly felt bad too, but still sent her to work in a brothel. Kieu said she did not want to go, but had to. She said, 'They held me like I was in prison.'"

She was kept there for three days, raped by three to six men a day. When she returned home, her mother sent her away for stints in two other brothels, including one 400 kilometers away on the Thai border. When she learned her mother was planning to sell her again, this time for a six-month stretch, she realized she needed to flee her home.