Bonnie Liltz was pronounced dead Saturday, the Cook County medical examiner's office said.
In 2015, when her health began to deteriorate, Liltz said she anxious her daughter Courtney, a 28-year-old with cerebral palsy, would be placed in an institution and not receive the care she needed.
Schaumburg police Sgt. Christy Lindhurst told the Tribune that her death is suspected suicide, but it remains under investigation.
Bonnie Liltz pleaded guilty in 2016 to involuntary manslaughter in the death of her daughter. Liltz had later said that she had cancer and feared for her daughter's future as her own health declined.
After serving several months of the term, her attorney convinced the court she was receiving inadequate health care and she was allowed to be released on bond. "We had a very nice conversation", Glasgow said.
Her daughter had cerebral palsy and needed constant care. The cause and manner of her death could be made available as early as the afternoon, if the results are not pending toxicology results, he said.
She adopted the girl because she was unable to have children of her own, the magazine reported. Authorities say she did leave a suicide note.
"The thought of her having to live in an institution for the rest of her life was more than I could bear", Liltz said in court, pausing amid bouts of tears, according to her lawyer.
"She's at peace now, in heaven with her daughter", Gladys Liltz said. "She just didn't want to die in prison". Tom Glasgow told People that Liltz wanted to spare her daughter the risk of being institutionalized. Seeing her stomach collapsed where it should be fuller, she believed that was exactly what was happening: She was dying, and she was out of options. But in the suicide note to her attorneys, Liltz wrote that she was exhausted of fighting and knew she wouldn't survive in prison.