"Today marks the 2,150th day since I was separated from mom," says 23-year-old Ri Ryo Gun, visibly emotional. "Not a day or two -- but six years."

One-way ticket

Ri's mother, Kim Ryon Hui, lived a relatively upscale life in North Korea until she went to China in 2011 to visit relatives and seek medical care for liver disease. She'd been hospitalized for six months in North Korea and had heard the treatment there was more advanced.

When she arrived, she discovered that Chinese doctors wanted cash for treatment up front and she couldn't afford the medical bills.

She says that little did she know, once she signed papers renouncing her North Korean citizenship, she'd never be able to go home. Once she realized this was the case, she told the broker handling her case that she wanted to escape, she says, but the broker took her passport away.

"Other defectors who were with me said if I go out and get caught they too will be handed over to China's Public Security and their life will be in jeopardy. Because I didn't have a passport, I had to follow them and I ended up in South Korea," she told CNN.

Kim says once in South Korea, she turned herself over to the police, pretending to be a spy in hope of being deported. But instead, she ended up in jail, sentenced for two years for passport fraud and espionage.

Visits and letters to the North are permitted, but only with the approval of South Korea's Minister of Unification, and her status as a criminal now makes any travel out of the country impossible.

Without government approval, the South Korean National Security Act stipulates that any contact or correspondence with what it defines as "a member of an anti-government organization" can result in up to 10 years' imprisonment.

This has been the case for tens of thousands of North Koreans who have fled to South Korea since the great famine of the late 1990s -- but Kim is one of the few who says she wants to return.

Video messages

In Seoul, we play Kim a video of her family in North Korea -- a rare opportunity for her to see her daughter who was just 17 when they were separated.

"I'm sorry for keep on crying, when I have to be strong in front of you," Kim's daughter Ri Ryo Gun says in the message.

Ri and her father, Kim's husband, tell her they have received a "great new house." "We hung the family photo and wait for the day you come back," he says.

It amazes Kim how adult her daughter, who has graduated from catering college, has become.

"She was a just a child playing in my arms and that's how I still remember her," Kim says through the tears, adding that she's "so thankful she has grown up to be a bright, confident young woman."

Kim says she takes comfort in the fact her husband and daughter are still young, but what really breaks her heart is being separated from her parents.

"During these six years my father has become an old man that I can't even recognize," she says when we play her a video message from them.

A bruised heart

Kim's father, Kim Se Hwam, and mother, Jo Won Hui, are both in their 70s.

Jo's eyesight is failing; she's already lost vision in one eye and is losing sight in the other. "What do we do if the daughter comes back when she can't see at all?" says her husband.

The elderly couple live on the 13th floor of an apartment block in Pyongyang. Because the lift is broken, they have to take the stairs.

They say they've received support from friends and the local community, insisting that in their country they "share sadness and tragedy."

But they say their health has suffered from the anguish they feel being separated from their daughter.

"My heart's been bruised," says Kim's mother. "My daughter asked me to stay healthy and please be there to hug me when she comes back, to please give her a hug, but what would it be like for her if she comes back after I pass away?"

We play them a video message and they say it's the first time they've laid eyes on her in six years.

"My aged parents, who should be just spending their last days looking at happiness of their children, and the oldest daughter is still making you sad, making you shed tears. I am so sorry," Kim says in a video message from across the border.

Defections

Kim's family deny this is the case, calling such stories "propaganda" and "rumors."

"There is no such thing as the government punishing us or looking at us differently. They would rather try to help us as much as they can," Kim's father says.

But for daughter Ri, ongoing tension on the divided Korean Peninsula isn't what matters.

"Putting all the politics and ideology aside," she asks, "as a human with love and affection, isn't a heart of a mother who wants to go back to her family, a heart of a person missing his or her parent, a basic right a human must have?"