She worried about the scale of the disaster. She worried whether she would ever be found. "You don't know if you stayed there, for a few hours, for days. You have no idea," she said.
As the waves subsided, recovery efforts were initially chaotic. Two Thai men eventually rescued the former Sports Illustrated swimsuit issue cover girl.
"One of the Thai men was so sweet because actually the water took everything, what I had on," said Nemcova. "He just left me some clothes and I asked him, 'Can I get your T-shirt?' And so I got his T-shirt."
Nemcova said she admired the rescuers because they went to work despite not knowing the fates of their own families, and because they had no idea if another wave would come in and kill them too.
"In that moment, people were thinking about others, not about themselves," she said. "They were ready to sacrifice their lives. And most of them, they lost their babies. They lost their wives, they couldn't see them."
Nemcova was transported to a hospital. She was placed next to a Thai patient, who gave her a small Buddha she wears to this day. "He said, 'It will protect you,' " she said.
Nemcova is now walking with crutches, but she is expected to recover fully. The long convalescence gave Nemcova a chance to look for meaning in the disaster.
"When it happened, it brought families together, it brought the countries together, it brought the whole world together for a moment," she said.
Even when she was healthy enough to do so, Nemcova had trouble leaving Thailand because she was sure that her boyfriend's body would be found.
"I was hoping and having a big hope," she said. "But slowly you have to … when the days they go by, you have to realize that he will stay in our hearts all the time for forever."
She says the waiting was one of the hardest parts -- "not knowing if Simon's still somewhere and needs help."
Sawyer asked Nemcova what she would say to Atlee if she could. "There are lots of things which I would love to tell him, but in some way, I also feel that I lost the person closest to me. And I got second chance to live. So in a way I feel that I live for both of us and I will do my best," Nemcova said.
She has not said whether she will return to modeling. "In the moment, I live day by day."