Cole announced in July that she was suffering from hepatitis C, a liver disease spread through contact with infected blood. She said at the time that the disease was revealed during a routine examination and was likely caused by her drug use years ago.
O'Connor said Cole had been responding well to treatment, but blamed the medicine she has been taking and a busy publicity schedule to promote her new album, "Still Unforgettable," with causing her problems. Cole had taped several TV appearances and had appeared live on NBC's "Today" show on Sept. 11, a day before her hospitalization.
Cole is expected to be in the hospital for a few more days and then will return to her home in Los Angeles, where she will be on bedrest, O'Connor said.
"We canceling her activities in October, but we do expect her to have a complete recovery," she said. "She just needs some rest."
O'Connor said Cole has been well enough to talk on the phone everyday, but didn't have much information on her condition.
Cole, the daughter of jazz legend Nat King Cole, has sold millions of albums in her own long career. Her best-selling work was her 1991 multiple-Grammy winning CD, "Unforgettable ... With Love," on which she remade some of her father's classics.