A suburban Chicago mother, who was due to report for her prison term Monday for administering a fatal dose of medication to her severely disabled daughter in 2015, has been found dead of an apparent suicide at her residence, authorities said Sunday.

Bonnie Liltz, 57, was found dead at her apartment in Schaumburg, Chicago, on Saturday evening. She had been sentenced in 2016 after pleading guilty to involuntary manslaughter in the death of her adult daughter. Liltz died at the same residence where she administered a fatal dose of medication to her 28-year-old daughter Courtney. Liltz had later said that she had cancer and feared for her daughter's future as her own health declined.

“It’s a tragic, tragic end,” her attorney, Tom Glasgow, said Sunday. “She just didn’t want to die in prison.”

She had recurring cancer and gave her daughter Courtney, a fatal dose of prescription medication on May 27, 2015. Tom Glasgow told People that Liltz wanted to spare her daughter the risk of being institutionalized.

Police went to her house on Saturday after family members called them as they had been concerned because they hadn’t heard from Liltz since Friday. Police said there was no evidence of foul play and suicide has been suspected, however, an investigation is still ongoing.

Liltz pleaded guilty to involuntary manslaughter in her daughter’s death and was sentenced to four years in prison by Cook County Judge Joel Greenblatt in 2016. However, Liltz was released on bond after serving a few months while appealing to the Illinois Supreme Court which declined to hear the case. Her lawyer had also argued that the medical care she required was lacking in prison, Fox News reported.

Last Tuesday, a judge ordered Liltz to return to prison to finish her four-year sentence for involuntary manslaughter. She had been scheduled to report Monday.

She adopted the girl because she was unable to have children of her own. She had Stage III ovarian cancer at 19 years of age and had undergone a hysterectomy.

In 2016, prosecutors accused Liltz of feeding her 28-year-old daughter a lethal dose of medication through the victim's feeding tube before trying to take her own life. She later flushed the medication with wine.

Her daughter had cerebral palsy and needed constant care. Liltz had said that she became desperate over the concern for her daughter’s health under someone else’s care.

Her attorney, Glasgow said that he talked to Liltz early Saturday and there had been no indication of any plans to take her own life. However, he said he had documents from two doctors that suggested she would die in prison if she was sent back. He also said that she reportedly left a note.

"It’s very upsetting to me because it could have been avoided," Glasgow said after hearing the news.

"She’s at peace now, in heaven with her daughter," Gladys Liltz, 89, her mother, told the Chicago Tribune. "That’s all she ever wanted was to be with Courtney."