By Tracy Jarrett, NBC News

Kidnapping victim Elizabeth Smart says she survived her nine-month ordeal by following her captors' commands and earning their trust, which ultimately helped set her free.

"Things that I'd always told myself I'd never do, I would do them if it meant I would survive. If it meant that one day I would be able to go back home and be with my family again, I would do it," she said during an exclusive interview with NBC News' Meredith Vieira.

Smart was 14-years-old when she was kidnapped from her Salt Lake City bedroom in the early morning hours of June 5, 2002. Her abductor, religious fanatic Brian David Mitchell, forced her to hike up the mountainside behind her home for hours until they reached a makeshift campsite.

In a Meredith Vieira Special that will air on NBC at 10 p.m. ET on Friday, Smart and Vieira went to the scene where that campsite once stood, and Smart remembered a strange woman in long linen robes ordering her to undress. It turned out to be Mitchell's wife, Wanda Barzee. Mitchell then began performing some kind of marriage ceremony.

"I was begging and crying and just so scared,'' Smart said. "I remember thinking, I know what comes after a wedding. And that cannot happen to me. That cannot happen."

Only a few hours earlier, she had been at home in her bed. Now Mitchell had her trapped.

"I remember him forcing me onto the ground, (and) fighting the whole way,'' she said. "And then when he was finished, he stood up, and I was left alone, feeling absolutely broken, absolutely shattered. I was broken beyond repair. I was going to be thrown away."

Mitchell later chained her to a tree, and months of abuse followed.

Smart was repeatedly raped, tortured, and threatened while in captivity. Early on, when Smart fought back against Mitchell's attacks, her captor only threatened her more. "He looked at me and he said, ‘If you ever scream out like that again, I will kill you. If it'll help you not scream out, I can duct tape your mouth shut,'" she recalled.

Smart came close to being rescued, once by her uncle and once when she was questioned by a police officer who had received a tip that Smart had been spotted, but Smart chose not to scream for help or try to run away—a decision she says people ask her about frequently.

"I was under threat of my life, I was under threat of my family's life.  And those two threats right there are stronger than chains for me," she said. 

The trauma and isolation made her feel hopeless at times. "If I could've slept for nine months, I would've," she recalled.  "That's where I could go to almost and not feel the pain, not feel the despair, not feel everything that was happening to me."

"There was a point that I stopped crying,'' Smart said. "It's not just because I didn't feel pain any more, not because I didn't feel sorrow. It was just to keep going. I mean, it just was to survive, to live."

But Smart turned to her faith and thoughts of her family in order to cope, she said.  "My family was still there.  And because of that, because I had that and because I knew that, I was able to make the decision to do whatever it took." 

Smart followed her captors' demands and tried not to upset them, hoping to earn their trust and convince them to release her from the tree to which she had been chained. Smart's plan worked, and Mitchell eventually decided to take her and Barzee—who he called his "wives"—to Salt Lake City in search of food and alcohol.

Afterwards, public outings became more regular, and the group even visited the public library to map out a route to California, where they moved for the winter. Mitchell concealed Smart's identity by dressing her in robes and a face-covering veil; however, Mitchell failed to cover his own face.

Months later, upon returning to Utah, at least two different couples spotted Smart and her kidnappers and recognized Mitchell's face from a sketch released by America's Most Wanted. The police were notified, and shortly after, the trio was surrounded by police. Smart was questioned and taken to a nearby police station where she was reunited with her family.

Seven years later, Smart testified against her captors, confronting Mitchell in court. He is now serving a life sentence, while Barzee is serving 15 years. 

Since her kidnapping, Smart has created the Elizabeth Smart Foundation to help prevent crimes against children and help other victims of sexual abuse. She's also gotten married—accomplishments she attributes to the support of her family.

"I had something worth living for, worth surviving for, that wouldn't change, that wouldn't fade or disappear, I made the decision I would do whatever it took to survive."

Smart has written a memoir about her abduction, "My Story," which will be published next week. 

She will also appear in an exclusive, live interview on TODAY on Monday, to talk further about her story. 

Scott Stump contributed to this report.