NYT:

In 1998 Ms. Sontag received a diagnosis of cancer, from which she recovered. Ms. Leibovitz took several months off to be with her. There are photographs of that period too, of Ms. Sontag receiving chemotherapy, having her hair cut. “You know, one doesn’t stop seeing,” Ms. Leibovitz said, when asked about her impulse to photograph illness. “One doesn’t stop framing. It doesn’t turn off and turn on. It’s on all the time.” In the middle of her Caesarean in 2001 she reached up with a camera to try to shoot the birth of her daughter, Sarah, over the curtain suspended across her midriff. “They’re all totally out of focus and terrible,” she laughed.

She photographed her father after his death in 2005. He was 91, had lung cancer and had driven a car until a week before. He died at home in bed, with hospice care, in his wife’s arms. The family kept his body in the bedroom all day, as children and, later, a rabbi arrived. Ms. Leibovitz photographed him there, his head on a flowered pillowcase, in pajamas with dark piping. “You find yourself reverting to what you know,” she said. “It’s almost like a protection of some kind. You go back into yourself. You don’t really know quite what you’re doing. I didn’t really analyze it. I felt driven to do it.”
She said, “My father was so beautiful lying there.”

Here.