Boston bombing survivor making good on a marathon promise

The Boston Marathon is the world's oldest annual marathon, but what happened on April 15, 2013 changed the historic event forever. Three people were killed and more than 260 were injured after a pair of bombs detonated near the finish line. Among the most severely wounded that day was Adrianne Haslet-Davis, a professional ballroom dancer who lost a part of her left leg.

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Her three-year recovery has been painful and difficult, but resilience and determination have her standing, even dancing, again.

This April, Haslet-Davis plans to accomplish what she says is her biggest challenge yet: completing the race she'd never dreamed of running.

"The milestones you've made running. What has that meant?" asked "CBS This Morning" co-host Norah O'Donnell.

"Gosh. It's meant the world to me," Haslet-Davis said.

She is making good on a promise to complete the Boston Marathon.

"Are you a runner?" O'Donnell asked.

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Adrianne Haslet-Davis and Norah O'Donnell go for a jog CBS News

"I am now," Haslet-Davis said, laughing. "Running for me was like torture. I mean, I would run a block and be winded and feel like I was going to die."

"And now you're missing part of your leg and you're running a marathon," O'Donnell said.

"Yeah," Haslet-Davis said.

"Think about that," O'Donnell said.

"Yeah. It's bizarre," Haslet-Davis said.

Bizarre because three years ago on Boylston Street, while watching runners make their way to the finish line, Haslet-Davis lost her ability to stand, let alone run.

"April 15 -- where were you when the blast occurred?" O'Donnell asked.

"So I had taken a right onto Boylston Street. And the finish line was behind me, and I heard a loud blast behind me," Haslet-Davis recalled.

She buried her head and put her fingers in her ears, she said.

"I knew -- and I still to this day don't know how I knew -- but I knew it was a terrorist attack. I knew another one was going to hit," Haslet-Davis said.

The next thing she knew, she was on the ground.

"I thought, 'Well, I don't have any experience in this, but there's no way you can live through something like this,'" Haslet-Davis said.

After her lower left leg was amputated, Haslet-Davis began a long and difficult recovery. As painful as it was, she documented the process in a CNN documentary.

"You know it was really important to me," Haslet-Davis said.

"Part of documenting your recovery, too, I'm sure it was cathartic for you," O'Donnell said.

"Yeah," Haslet-Davis said. "I was thankful that it was as raw as it was, and that I captured those raw moments. It's really important to me. I wanted to be emotionally as honest as possible."

"What was it like to stand on your own for the first time?" O'Donnell asked.

"Gosh, that moment was amazing," Haslet-Davis said. "I remember standing up and the walker was in front of me. And I remember standing up and then just as anyone would, you adjust your shirt at the bottom, and I had both hands free to do it. And I, just out of instinct, adjusted my shirt. And then I immediately-- like, I remember seeing it in the video and I immediately-- just you could see the emotion build up and I put my hands in my face and just lost it."

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Adrianne Haslet-Davis is overcome with emotion as she stands on her own for the first time CNN "The Survivor Diaries"

Haslet-Davis' difficult days mixed with milestones. The professional dancer made her way back on stage.

But with success came hardship.

Haslet-Davis and her husband, Adam Davis, who was also injured during the bombings, began their recovery together, but have since separated. She told us they agreed not to discuss their split publicly.

Haslet-Davis said her life has changed in "every way possible."

"I look at life so differently now. I'm more patient with people. I didn't think I was impatient before. But I'm more patient with people," Haslet-Davis said.

"Are you still angry?" O'Donnell asked.

"Yeah. I am. I will always hold onto that. ... I've learned that running really helps with that in a good way," she said. "But I believe in feeling every bit of that and not burying it. So that you can really enjoy the good days."

"I like that you said, 'My life is not going to be defined by what has happened to me,'" O'Donnell said.

"Yeah. Yeah, I want my life to be defined by how I live it," Haslet-Davis said.

"I'm not just an amputee. I'm not just a marathon survivor. You know, none of us are," Haslet-Davis said, walking toward the finish line. "And I think it's important to always remember how far you've come as well. Because I have days where I think I haven't come far at all, which sounds crazy to say, but you get in these mindsets. And it's important to see, you know? To see how far you've come."

Haslet-Davis' run will mark a personal goal, but she's also doing it to support the efforts of Limbs for Life, an organization that provides life-changing prosthetics for fellow amputees in need.