Sara Packer and Jacob Sullivan face almost two dozen charges including criminal homicide, rape and abuse of a corpse.
Packer, 41, is charged with criminal homicide, rape conspiracy, kidnapping and abuse of a corpse, among other charges.
Sullivan and Packer have both been charged with murder while Sullivan was also charged with kidnapping and rape, according to reports.
Bucks County District Attorney Matthew D. Weintraub said that Grace suffered terribly before dying, called her killing "a rape-murder fantasy that was shared by Jacob Sullivan and Sara Packer, and they acted it out".
She had been charged with endangering the welfare of children and obstructing the administration of law and was being held at the Montgomery County Correctional Facility in lieu of $10,000 bail.
"Then she was poisoned from medication and left for dead", added Weintraub. Police also learned Sara Packer had been receiving $712 monthly for care and custody of Grace, and that on August 22, Sara completed a Continuing Disability Review Report related to Grace, never disclosing the girl's disappearance.
On Sunday, Weintraub also confirmed a third woman, who was involved in a polyamorous relationship with Packer and Sullivan, was also being questioned as a person of interest in Grace Packer's death.
Sullivan admitted to healthcare workers at the hospital that he was responsible for Grace's murder and that Sara Packer was his accomplice.
The couple entered into a suicide pact, and tried to kill themselves by overdosing on drugs on December 30, the complaint says.
Six months after the mysterious disappearance and subsequent death of 14-year-old Grace Packer, Police officials investigating the case have managed to solve the murder mystery.
Packer reported her daughter missing in July. Her remains were found on Halloween 2016.
Sullivan told police he and Sara Packer drove Grace Packer to the new Quakertown residence on July 18, walked her inside and he struck her in the face several times.
However, according to court documents, a week later Sullivan told hospital personnel he wanted to "confess everything" about the Grace Packer killing, then did so on Saturday.
Sullivan was hospitalized on Dec 30 when he was found unresponsive from a prescription drug overdose at his Horsham home in an apparent suicide attempt.
She was then allegedly raped by Sullivan while her mother watched. The two killed Grace in July, and then hid her body in the attic of their rented home in Quakertown, Pa. for almost four months and later dismembered it, officials said. She lied that Grace was still alive so she could collect her social security checks. A pathologist determined that the arms and legs had been forcibly removed from the torso, and the cause of death was pending further investigation.
When the pair returned the next day and Grace was still alive, Sullivan strangled and suffocated her, then packed Grace's body in cat litter to mask the odor and left it in the attic for three months, the District Attorney's office said. A detective on Aug 24 found JP enrolled at the Quakertown School District but not Grace. Grace was then allegedly tied up, gagged, and left to die in the hot attic of the house, investigators said. He is scheduled for a preliminary hearing on January 20.