Olga Murray laughs when she's called a modern-day abolitionist. It is, however, a fair description.

This 82-year-old retired lawyer from California now spends half of her time living in Katmandu, Nepal, where she works to free child slaves.

"It's very difficult to think that in the 21st century, this is a practice," said Murray. But, she argued, "it's happening all over the world, and a lot of people don't know about it."

Watch ABC's investigation into modern-day slavery Tuesday on "Nightline" at 11:35 p.m. ET and click HERE to learn what you can do to help end slavery.

With her silver hair and fair skin, Murray stands out in Nepal, a poor, landlocked country sandwiched between China and India. With remarkable ease she navigates the chaotic streets of the capital, where painted yogis and sacred cows are common sights.

She is no tourist. She and her organization, the Nepalese Youth Opportunity Foundation, have come up with a remarkably simple and successful method of liberating hundreds of young, female slaves.

'It's Not Because They Don't Love Them'

More on that solution below. First, the problem: For generations in Nepal impoverished families from the countryside have been selling their daughters to wealthy families where the girls, known as "kamlaris," are forced to do housework.

When asked why parents would sell their children, Murray explained, "It's not because they don't love them. It's like they have no choice. Sometimes it's a choice between selling their girl … and feeding the rest of their family."

The practice has become so widespread and socially acceptable that we were able to meet and interview slave girls and their owners.

We found Bijani Chaury, an adorable 12-year-old, in the well-appointed home of Ejopal and Sartoshi Oli, a teacher and a housewife, in Katmandu.

Bijani's life bears little resemblance to the plantation-style slavery of pre-Civil War America. There are no chains or farm labor. She is, however, forced to work under threat of violence and for no pay beyond subsistence, which is an internationally recognized definition of modern-day slavery.

According to the non-profit group Free The Slaves there are an estimated 27 million slaves in the world right now -- more than at any time in recorded history.

Bijani told us that she spends her day cleaning the house, making tea and helping her Mrs. Oli prepare meals. She doesn't go to school. And, she said, she misses her parents and sisters, who are back home in rural Nepal.

Mrs. Oli insisted, "We love her like our own daughter."

Preventing Servitude

While Bijani bore no outward signs of abuse, many former kamlaris have reported being beaten, humiliated and raped.

Enter Olga Murray and her colleagues. They have come up with a way of preventing parents from sending their children into servitude.

"We say to the family: If you allow your girl to come home, or not sell her again … we're going to give you either a baby piglet or a baby goat. And we will put your daughter in school and pay all her school-related expenses. Everything. Which comes out to about $50 a year."

These seemingly small gestures -- paying for school and giving families animals they can later sell for a profit -- can remove the economic incentive to sell daughters into slavery.

In the areas where this program has been tried, Murray says the kamlari system has essentially been eradicated.

"I can't tell you how satisfying it is," Murray said.