Debbie Leitch, a Down’s Syndrome woman, was discovered emaciated inside a property in Blackpool, Lancashire, by emergency personnel on August 29, 2019.
Leitch died of emaciation and neglect, and a post-mortem test revealed that she had a scabies skin infestation.
Six people have been arrested in connection with her killing.
The deceased’s mother, Elaine Clarke, was charged with gross negligent manslaughter and admitted the charge at Preston Crown Court on Friday.
Clarkehad previously pleaded not guilty to killing her vulnerable daughter but changed her plea just 10 days before the case was due to go to trial.
Clarke has been remanded in custody ahead of her sentencing on February 7.
Earlier, her former 45-year-old partner Robert Bruce from Leeds, West Yorkshire, was charged with allowing or causing the death of a vulnerable adult. The charges were later dropped.
Judge Amanda Justice Yip told Clarke: “You are well aware of the inevitable outcome that you will be going to prison, and I think the time has come that I am going to remand you to prison to make sure you are here on time on the next occasion.
She added: “As far as (Bruce) is concerned, a not guilty verdict has been entered and (he) will be released.”