It wasn't that the shoulder wouldn't heal in time, it was more the fact that if she had one crash in training she would be gone, yet she couldn't avoid training. It was a classic Catch 22.
"I had no choice," Walker said. "I was scared every time I rode my bike up until two weeks ago. Sometimes I would do jumps, I would have a close call and I would just cry.
"I was living right on the edge of being a medallist or not even being at the Olympics.
"If I wanted to play it safe I could have been an Olympian again but I wouldn't have been on the podium.
"I had to risk my body, I guess, and the Olympics, every day I was on my bike."
It is not easy being perched on a bicycle at the top of an 8m ramp that tricks you into thinking it is a sheer drop. As you peer into the distance, you see the first banked turn and years of experience start telling you eight into one won't go.
Approaching this turn, you are asked to think counter-intuitively; you have to be prepared to crash to win. If you back off even slightly to avoid potential crashes, you're gone. In a 37-second race, you don't have the time or space to make up lost ground.
You can't ride scared, but Walker freely admits it is something she has done too often in her career.
The skills have never been in question - Walker is a superb technician - and neither has her physical strength. It's the mental strength that has held her back.
"Going into Beijing I did doubt myself a lot. I didn't really believe that I could win, or that I did deserve to be on that podium.
"I've worked a lot over the last two years to build up the confidence in myself and the belief in myself that I can do this and that I can push myself."
Walker said she was afraid of losing and that had become her primary motivation, rather than being motivated by a desire to do your best.
That's why she has employed the services of David Galbraith. The sports psychologist has worked with the Chiefs and the Magic this year, so has the Midas touch at present.
"Almost every week I would see him. I've been working really hard on learning what the best way to prepare for a race is for me."
Walker can get caught up in the moment - like she did in the first of the best-of-three semifinal. At the top of the ramp the old fears returned.
"I got scared, a little bit blown away by the whole thing," she recalled.
Walker finished fifth in that race and needed a fourth and a third in her next two races to make the final. Only four riders from each semifinal went through and Walker, 24, was fourth.
"I ride fastest when I'm focused and thinking about things that have no emotion involved in them. On the day I think about rolling my wrists forward and getting my body position in the right place, my breathing; real simple stuff and it takes up my thinking space so I can't get emotional, which is what I lacked in the first race [of the semifinals]."
For the one-off final, her mind was clear, her start was sensational and her rounding of the first corner fearless. Only Pajon - unbeaten all day and in the form of her life - was better.
For some people, silver means second. For Sarah Walker it means an awful lot more.
