updated 10/30/2012 AT 6:00 PM ET
•originally published 10/30/2012 AT 6:30 PM ET
Rehearsing for the country-themed night Johnson, 20, re-injured her knee, giving her a painful reminder of how her Olympic career ended.
“It took me back too much,” she told PEOPLE backstage after the dance. “The first thought I had was the Olympics. I mean I lived two full years in training just constantly having to deal with pain, and push it out of my mind, being as that’s what took me out of the Olympics. Feeling that again was devastating.”