When she left as a finalist three months ago to work on losing weight at home, she was 150 lbs. Between then and the finale, she lost 45 more.
It was the latter that shocked Jillian Michaels and her Biggest Loser trainer counterparts as much as it did longtime fans of the popular NBC competition.
"What people don't understand is, when the contestants leave to go home … they're in charge of themselves," says Harper, 48, of the show's process.
"So, I had not seen her until that night, and so when she walked out, I was just kind of like, whoa. And I’ve been on the show since the beginning, forever."
Frederickson, who has faced major scrutiny this week, worked on the show with trainer Dolvett Quince, who wrote in a Facebook message Wednesday:
"Please try not to look at one slice of Rachel's journey and come to broad conclusions. Rachel's health is and always has been my main concern."
"Her journey to good health has not yet ended!" Quince added.
Many critics of the show say she is too skinny at 5'4" and 105 lbs. She says she worked out four times a day, but is now in "maintenance mode."
For her part, Frederickson is happy with her new body, saying "I just love myself, and I am embracing it," while her "goals are to be healthy and strong."