Greubel, 30, had been a track star at Cornell - earning an NCAA spot in the heptathlon. But she never dreamed of being an Olympian until after her 2007 graduation, when a teammate suggested her competitiveness and strength made her well-suited for bobsledding.
"Once I started doing it, and my body finally got used to it, I started considering the real opportunity I had in front of me," she said during a recent telephone interview from the team's pre-Olympic training facility in Italy.
"This was an Olympic sport, and you didn't have to be competing in it your whole life to have a chance. Until then, the Olympics had always seemed like a separate entity. Olympic athletes were like movie stars to me. I'd go see them in movies, but I never made the connection that it could be me."
Greubel is the oldest of four children. Her father owns a Bucks County landscaping firm, and her mother is a neonatologist at Children's Hospital of Philadelphia.
A graduate of the Hun School in Princeton, she grew up competing fiercely with her brother Eric, three years younger, in everything from tennis to card games to horseback riding.
"Everything felt like it was a fight to the death," she said of their rivalry. "Left unattended, we would soon be dueling with pitchforks and whips."
After graduating with an animal science degree from Cornell and taking her first bruising bobsled rides, Greubel enrolled in a graduate program at Lesley University in Boston.
Sports, whether track, show-jumping, basketball, or field hockey, had always been a vital part of her life, and she wasn't ready to abandon them.
"But I wasn't sure that bobsled was something I wanted to pursue," she said. "Then the [driver] who had given me my first ride down a track called and asked if I would compete in two America's Cup races with her. I did, and I was completely hooked."
Bobsled can't be practiced on a simulator, so the only way to gain experience is by hurtling down tracks, most of which are in Europe.
"That first year was tough," Greubel said. "Crashing isn't a lot of fun. You have to be resilient. You learn by doing it. You learn by your mistakes."
Greubel began her career as a brakeman, or pusher, but after just failing to make the U.S. team for Vancouver in 2010 - she was an alternate - she jumped into the driver's seat.
"I didn't want to wait another four years for someone to take me with them," she said. "I wanted to be the one in control."
As she and the American women have gained experience, and added ex-track stars such as Lolo Jones as pushers, their world ranking has improved.
Last month Greubel teamed with ex-Olympic sprinter Lauryn Williams in Austria to capture her first World Cup gold medal. Earlier in the season, partnering with two other track stars-turned-bobsledders, Jones and Aja Evans, she piloted her sled to three bronzes and a silver medal.
Which of the three she'll be teamed with at Sochi hasn't yet been determined.
"All of our brakemen are so strong and fast," she said diplomatically, "I'd be thrilled to have any as a teammate."
Whatever the three U.S. pairings, they all figure to be strong medal contenders.
"Women's bobsledding has only been in the Olympics since 2002," Greubel said. "It's been evolving. We're competing against women who have been driving 30 years between bobsled and luge.
"Our big advantage is having such great athletic talent on the team and having really big pushes. That helped us stay competitive until the last couple of years, when our skills have really improved."
For all America's improvement in the sport, bobsledding isn't yet basketball. Greubel has had to work as a waitress to support herself the last five years and recently began soliciting sponsors on the Internet.
In the meantime, with all the free time between runs that are over in roughly 11/2 minutes, she's undertaken an extensive weight-training program and added 20 pounds to her 5-foot-9 frame.
"You need to move mass," she explained. "Bobsledders want explosive power, so we train like weightlifting sprinters."