But she also said the film unfairly shows her mother, Vivian Liberto Distin, Johnny Cash's first wife, as a shrew. Actress Ginnifer Goodwin plays her in the movie.
"My mom was basically a nonentity in the entire film except for the mad little psycho who hated his career. That's not true. She loved his career and was proud of him until he started taking drugs and stopped coming home," Kathy Cash said.
Vivian Liberto Distin died earlier this year as a result of complications from lung cancer. She and Cash were married 13 years and had four children together. He pledged to remain faithful to her in his song "I Walk the Line."
Kathy Cash also said the movie fails to include any meaningful scenes with the children or show the pain she and her three sisters endured during their father's fight with drugs and their parents' divorce. She says it portrays Johnny Cash's father too negatively.
"Anyone who wants a good sex, drugs and rock 'n' roll movie is gonna love it," she said. "I'm anticipating dyed-in-the-wool fans objecting to a lot of stuff."
John Carter Cash — Johnny and June's only child together and an executive producer for "Walk the Line" — says his half-sister's criticisms have merit. But he says it's OK to take some license and that, in the bigger picture, the movie succeeds in telling his parents' love story.
"I'm compassionately understanding," he said, adding, "the point of the film is my parents' love affair."
"Walk the Line" is produced by 20th Century Fox, which is owned by News Corp., the parent company of FOXNews.com.