A Mississippi Circuit Judge on Monday told an ex-cop who pleaded guilty to having sex with her supervisor while her 3-year-old daughter was dying in a hot patrol car that "you will forever be entombed in a prison of your own mind.”

Cassie Barker, 29, pleaded guilty to manslaughter in a plea bargain after being indicted on a second-degree murder charge. Barker had been free on bail but was arrested Monday after pleading guilty.

Her daughter, Cheyenne Hyer, died Sept. 30, 2016, after Barker left her strapped in a car seat for four hours while she was with her then-supervisor at his home.

Barker later found her daughter unresponsive. Authorities said Hyer's body temperature was 107 degrees when she arrived at a nearby hospital. The heat index that day had reached over 100 degrees, the Sun Herald reported.

I don’t know what I could ever do to you that could be worse than what you’ve already experienced … You will forever be entombed in a prison of your own mind. — Harrison County Circuit Judge Larry Bourgeois

Prosecutors recommend that Barker spend 20 years in prison, according to the Sun Herald. Harrison County Circuit Judge Larry Bourgeois said he wanted more time to consider the case and would sentence the ex-Long Beach officer on April 1.

“I don’t know what I could ever do to you that could be worse than what you’ve already experienced … You will forever be entombed in a prison of your own mind,” Bourgeois said to Barker.

Barker, who was working two jobs when her daughter died, originally claimed she had been talking to her then-supervisor Clark Ladner at his house early on a hot weekday morning when she fell asleep.

Ladner and Barker were fired by the city of Long Beach within days. Ladner told officials he didn't know the girl was in the car and hasn’t been criminally charged.

The mother had left her daughter alone in a car at least once before, at a store in nearby Gulfport in April 2015. Police responded and child welfare officials took temporary custody of the girl at the time. Barker was suspended from the Long Beach police for a week without pay. The girl's father, Ryan Hyer, said he was never notified of that first incident.

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"Every time I close my eyes, I picture her suffering and then I picture her laying in this coffin," Ryan Hyer said Monday. "I still see her smiling and laughing in my head and I would assume that smile and laughter turned to pain and suffering in that instance."

The father is suing the Long Beach Police Department and the Mississippi Department of Child Protection Services for the wrongful death of his child, saying the child welfare agency should have taken stronger action after the first incident.

"As a parent, you are supposed to protect your child, and Cheyenne is gone because her mother didn't protect her, not once but twice," Hyer said.

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Barker herself was hospitalized after the girl's death for what officials described as shock. A psychological exam showed Barker suffered from post-traumatic stress disorder attributed to childhood trauma and her daughter's death. She was found competent to stand trial.

The Associated Press contributed to this report.