Sofia Vassilieva shaved off her hair and eyebrows to play Kate Fitzgerald. She described it as the least she could do to understand Kate's pain. She was filming this movie and Medium (2005), so she wore a wig for the show.
Although Cameron Diaz's character in the movie shaves her head, Diaz does not do so in real life. Sophia Vassilieva, who played Diaz's cancer-stricken daughter, did, however, shave her head in both the movie and in real life.
Real-life sisters Elle Fanning and Dakota Fanning were originally set to play Anna and Kate Fitzgerald. Elle bowed out after Dakota reportedly refused to shave her head, as required for the part.
This movie is based on the book "My Sister's Keeper" by Jodi Picoult. In the book, Anna wins her court case. Then, while driving to the hospital with her attorney, they have an accident that leaves Anna's brain dead. Her lawyer, who now has power of attorney, permits her organs to be donated to Kate, who makes a full recovery and goes into remission.