Amber Hilberling was serving a 25-year prison sentence, convicted of second-degree murder in the death of her husband, Josh Hilberling, when she was found hanging in her prison cell on October 24, 2016. Hilberling, who was 7 months pregnant at the time of her husband’s death in 2011, had maintained her innocence, saying that she pushed Josh in self-defense during an argument and he fell backward through the window of the couple’s 25th-floor Tulsa, Oklahoma apartment.

In an exclusive interview with Dr. Phil airing Monday, Hilberling’s mother, Rhonda, says, “I knew Amber was sad, but Amber was sad the entire time she was there. She was an innocent girl in prison and did not know how to play this game, what she used to call ‘play the game.’”

The Medical Examiner ruled Hilberling’s death a suicide, but her parents are not convinced their daughter took her own life.

WATCH: Parents Of 25-Year-Old Who Died In Prison: ‘We Found Out That She Hung Herself On The News’

“She wasn’t suicidal,” says Rhonda, who says she spoke with her daughter on the phone every day and visited her 25 times a year.

Rhonda’s husband and Hilberling’s stepfather, Bryan, adds, “The night before, talking on the phone, the whole conversation, she was talking about things happening in the future, and what [her son] Levi was going to be on Halloween.”

WATCH: Parents Of Amber Hilberling Say They Believe She May Have Been The Victim Of Foul Play

On Monday’s episode of Dr. Phil, hear how Rhonda and Bryan say they learned about their daughter’s death, and, why they believe she may have been the victim of foul play. Check here to see where you can watch.