Carole "Cookie" Cole's cause of death was not reported, but Timolin Colin, Natalie's younger sister, told the Post, Carole had a "cancerous spot."
"Our sister Cookie hadn't been to a doctor in 30 years, and last week she went in and they found a cancerous spot on her lung," Timolin told Page Six. "They had wanted to start chemo right away, but Cookie said no."
Natalie, who has hepatitis C and was undergoing kidney dialysis three times a week, was at her sister's bedside when she got the news that a kidney was available.
"She said, 'What do you mean? I can't deal with that right now! I'm here with my dying sister!' And they said to her, 'No, ma'am. We've got to do it now. You've got to be at Cedars-Sinai in two hours," Timolin noted.
Natalie had the surgery – a success — at Cedars-Sinai Medical Center in Los Angeles.
She is expected to be released over the weekend.