The daughter of a military official, she is not your typical defector - it was curiosity not desperation that pushed her to venture beyond its borders. Almost 20 years on, she has become a powerful voice of dissent, laying bare the reality of life under the totalitarian regime in her memoir The Girl With Seven Names. Now she is campaigning for greater protection for North Koreans who manage to flee - particularly women - warning that many are captured in China and sold into prostitution or end up in forced marriages.
Ms Lee says: "They are so humiliated and broken, they don't want to speak out, so I decided I should try to help. The Tumen and Yalu rivers act as a border with China. In some parts, the water is navigable, while in winter they are frozen over completely.
For many, the physical act of crossing is the easiest bit. There is no asylum once they reach the other side. They are regarded as illegal migrants and face deportation if caught and then severe punishment in North Korea.
The women are in an incredibly vulnerable position, Ms Lee says. They have little choice but to trust the brokers smuggling them out. But there is no one to turn to if things go wrong. Ms Lee herself narrowly avoided being forced into the sex trade when she crossed into China.
She was told she was being trained to work in a hair salon but on arrival she discovered it was a brothel, and managed to run away. North Korean women are also trafficked as "forced brides", she says, usually sold to men in the countryside. The combination of China's one-child policy and a historic preference for boys has now led to a shortage of women of marriageable age. Families are willing to pay hundreds of dollars for brides for otherwise ineligible bachelors.
