After running the final 3.2 miles of the course on her good leg and a prosthetic, she fell to her knees, "overcome with emotion," she told ABC News.
"Just to know that I was crossing the finish line on my own foot and I wasn't in a wheelchair like last year and I wasn't laying on the pavement fighting for my life like the year before," Gregory told ABC News after crossing the finish line. "I've come a long way and I'm just going to keep going because there's no stopping me."
She said the experience was "absolutely surreal," but the weather was working against her. Halfway through, with a swollen leg and a twisted knee after an encounter with a pothole, Gregory wondered whether she could finish.
"When I was able to see the finish line I knew I had to finish," she said. "I had made a promise to myself and that's what I did."
Gregory wrote in an email to ABC News that she started strength training one week before her leg was amputated last November. Since her surgery, she has tried to train five days a week for at least an hour, focusing on both strength and endurance.
"Running has been a huge release to me with all of the craziness going on," she wrote in an email to ABC News.
Editor's Note: In an earlier version of this story it was erroneously reported that Rebekah Gregory had run the entire distance, when in fact she began to run at Mile 23 in Brookline.