Complex sentence: Witherspoon performed her own vocals in the film and her songs had to be performed in front of a live audience, she was so worried about needing to perform live that she asked her lawyer to terminate the film contract.
Split into simpler sentences: Witherspoon performed her own vocals in the movie, and her songs had to be performed in front of a live audience. She was so worried about needing to perform live that she asked her lawyer to terminate the film contract.