"In last week's dance, in the dress rehearsal, I actually displaced a rib," Stirling revealed during a pretaped package. "Now this week, [I'm] trying to find the balance of taking it easy and yet rehearsing."
For Stirling, taking it easy isn't an option she's interested in.
"I have to do things full out if I'm gonna know what it feels like to do them in the performance, and yet I've got this rib that I feel in pretty much every movement," Stirling explained.
The intense agony of her displaced rib, and her utter disappointment at the possibility of having to bow out of the season, brought the 31-year-old musician to tears.
"I came in early today so I could rehearse, because I don't feel ready, and I can't even rehearse because I'm in so much pain," she told Ballas as she cried in the rehearsal studio.
Ballas didn't want to take any chances, so he brought her to urgent care to see how bad the damage really was.
"I'm gonna be so mad if I've blown it. We've worked so hard," Stirling said as they waited for results in the doctor's office. "I push, push, push all the time. It's how I've gotten to where I'm at. But I'm just so afraid that I might have pushed too far."
Despite the discomfort, the energetic star and her partner hit the DWTS stage with style and intensity for a Mexican Day of the Dead-themed paso doble set to Stirling's own song "Roundtable Rival."
The dance -- which incorporated traditional paso doble techniques with elements of irish folk dancing -- was fast-paced and included some truly impressive dance moves, including an amazing knee-walk across the floor.
After the dance, Stirling was clearly hurting and Ballas even kneeled down to Stirling could sit on his leg as a bench to rest and catch her breath.
"I'm in pain. I'm not gonna lie," she told co-host Tom Bergeron, breathing hard. "I think the paso doble is a beast."
"The paso doble is not the beast, you are the beast," judge Carrie Ann Inaba said, praising Stirling for her passion. "Because that was a really difficult routine, and I could see the pain you were in the whole time. While I saw it in your face, and sometimes in your back, I did not see it in the movements. You were able to execute those shapes with strength and bravery and conviction."
"That was so ambitious and totally intriguing," judge Bruno Tonioli marveled. "The speed of the dance was impossible even if you feel well, and you managed to do it, so great [work]."