Mills -- who has a prosthetic leg and two metal plates in her pelvis -- has been able to practice her dance routines only a few hours a week, compared to nearly 40 hours for the other celebrity contestants, the London Daily Mail reported Thursday.
"I rehearsed for only three hours last week because my pelvis was really hurting," she said. "I thought I can push myself to a degree where my pelvis starts causing huge problems or I can take it easy. I decided against pushing too hard so I could only do three hours."
The estranged wife of former Beatle Paul McCartney -- who lost half her left leg in a 1993 car crash -- said she had gotten a jump on learning the mambo before the show started. However, she added, "I doubt I'll stay in the show that long."