A Wisconsin mother stands accused of neglect after her 13-year-old daughter — whose rare medical condition left the girl unable to speak or walk — was discovered dead in their rotting home last year, according to multiple news outlets.

On May 29, 2017, Brianna Gussert’s body was found curled in her bed by Appleton authorities, according to the Appleton Post-Crescent. Brianna was wearing an old diaper that weighed 1.25 lbs and, investigators say they learned, she had apparently gone without care for days until she died.

Her date of death is believed to be around May 24, 2017, but it was not reported until five days later, on Memorial Day, the Post-Crescent reports.

Brianna was found after police responded for a welfare check at the house she shared with her mother, Nicole Gussert, local TV station WLUK reports.

On Monday, Nicole was charged with one count of child neglect resulting in the death of her daughter, according to the Post-Crescent.

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In a 17-page criminal complaint, the police officer who discovered Brianna described the inside of their home as having a “smell in the air of rotten food, human waste and death,” according to the Post-Crescent. The residence was full of trash and dirty dishes, as well as clothes, and fruit flies were seen upstairs.

Brianna died primarily of sepsis as a result of her alleged mistreatment, court documents state, according to WLUK.

Outagamie County District Attorney Melinda Tempelis reportedly described what the teen suffered as “a slow death.”

She was born with Wolf-Hirschhorn syndrome — a genetic disorder affecting a person’s development and growth, among other characteristics — which left her unable to speak and needing constant care, her father, Greg Gussert, told the paper.

“Nicole does not recall the last time she fed her [Brianna],” Tempelis alleged in court on Monday, according to WLUK. “She does not recall the last time she changed her diaper. She had not been bathed in over a week. She had not been cared for or checked on.”

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Though Brianna’s feeding tube was nearly empty when police arrived at the home, six boxes of formula sat on the porch outside, the Post-Crescent reports. Nicole allegedly told authorities that her daughter had not been to school in months, likely in part because Nicole did not want to get her ready each day.

“Some of the worst news I’ve ever heard. It’s unbelievable what she had to go through,” Greg told WLUK. At times he was in tears listening to what was said in court.

In addition to the neglect charge, Nicole faces three counts of possession with intent to deliver amphetamine, according to local station WGBA.

Nicole’s attorney, Robert Welygan, noted that the case against her remains unproven and is “simply allegations,” according to WLUK.

‘Happy All the Time’

Despite her health challenges, Brianna communicated with her facial expressions, her dad told the Post-Crescent. She cheered for both the Green Bay Packers and Milwaukee Brewers and played in a baseball league for children with disabilities.

She was buried on her 14th birthday, the paper reports.

Greg told the Post-Crescent that Brianna lived with Nicole, his ex-wife, because his apartment could not fit the the adjustable bed their daughter needed.

At the time of her death, Greg told the paper, he and his fiancée were about to buy a house that could accommodate her.

“This is a tragedy,” he said. “It’s a child who was taken away from her father, from her sisters, from her grandparents, from teachers and friends. She was taken too soon. She was such an inspiration and a wonderful child. And happy, she was happy all the time.”

Nicole is being held in lieu of $300,000 bond. It is unclear whether she has entered a plea.

Neither her attorney nor the Outagamie County District Attorney’s Office could be reached by PEOPLE on Wednesday.