Ma Lay Lay is a tiny, quiet woman. She doesn't smile much; she seems to have the cares of the world on her shoulders. She stares into the middle distance as all round her, her decision bears its fruit.

Born in Thailand, her parents left Myanmar in 1988 due to civil unrest, and her home became a huge and crowded refugee camp called Mae La, just over the border in Thailand. Seven years ago she registered as a refugee, and a few years later she met Christopher at school in Mae La refugee camp, the only home she's known in her 24 years.

"I fell in love with him. I liked his mind-set and his will, she remembers. Two children followed: Labur Paw (now 3) and Yewar Mar Ser (11 months).  And then came the bombshell that she had been accepted for resettlement to the USA and would leave in late September under a programme run by the US Bureau for Population, Refugees and Migration. In doing so, she became the 100,000th refugee that IOM has helped to leave Thailand since 2004 when large-scale resettlement operations resumed. The majority of them have come from nine camps on the border with Myanmar.

Now the day has dawned. "Even though I am very sad I will go because of the future of my children," Ma Lay Lay says as she prepares to leave the small wooden house that is the family home. "They will have a higher education and I will have an opportunity to work."

But getting there – taking a plane with two tiny kids, not being able to speak English, not having a home or a job – all those things weigh hard on her mind. And because her husband was not registered along with her he has to wait behind, and hope that his refugee registration will be fast-tracked successfully.

She feels she will cope for a time without her husband, but says "I'm worried that I don't know the language. I'm worried I won't be able to pay the rent, and I'm worried that I will get lost in the city and not be able to find my way home." But she's not worried about the cold. "As long as we have enough jackets I am not scared of the snow."

To make her move as smooth as possible, IOM has helped her on every step of the way. She and her children have had medical screening to ensure they are healthy for the journey. They have been shown videos on life in America, learned about the seasons, about American families, and even tested cookers, showers, taps and a toilet in a purpose-built "cultural orientation" unit run by the International Rescue Committee Resettlement Support Center.  Other organizations, including UNHCR, the United Nations High Commissioner for Refugees, have helped by providing protection in the camp over the years, then identifying and submitting their cases to the US for resettlement.

The orientation continues up to the moment that Ma Lay Lay and her children get on the plane, and beyond. IOM staff, fluent in her Karen language, show her and the rest of the group of people being resettled how to pack their bags, how to fasten a seatbelt, even how to use the aeroplane toilet.

Her children receive their first warm jackets, cool new sports shoes for the three-year-old, and diapers for the baby. They spend their first night in a hotel, with running water, flush toilets, a huge soft bed, air conditioning and electric lights. After their last orientation lecture they are waited on by hotel staff and then it's time for a short sleep before the 2am bus to the airport.

The old people are in the group appear to be in shock. The parents are worried, barely talking. Only the teenagers seem relaxed, laughing and smiling, already Americans in their minds. The international airport has everyone in awe – eyes wide at the high mirrored ceilings, the smart shops, the escalators.

We ask Ma Lay Lay what were the last words her husband said to her?

"He said 'I bid you farewell. Please go ahead and one day, if I have a chance we will be meeting again.'”

"But I woke up happy this morning," she says. "When we left the camp I saw trees and hills, a pleasant view. We are not being separated by death so our family doesn't cry – we feel positive energy in our minds."