A 25-year-old Oklahoma woman convicted of second-degree murder for pushing her husband to his death from the 25th floor of their apartment has been found dead in her prison cell.

Oklahoma Department of Corrections spokeswoman Terri Watkins says Amber Hilberling was pronounced dead at 5.33pm Monday at the Mabel Bassett Correctional Center, where Hilberling had been serving a 25-year prison sentence for the 2011 death of her husband, US Air Force veteran Joshua Hilberling.

Watkins says the state medical examiner's office will determine Amber Hilberling's cause of death.

Amber Hilberling, 25 (left and right), who was convicted of second-degree murder in 2011 for pushing her husband (pictured together right) to his death from the 25th floor of their apartment, took her own life in prison

The 25-year-old inmate was pronounced dead at the Mabel Bassett Correctional Center in Oklahoma Monday evening

Young mom: Hilberling, who turned 25 on October 1, leaves behind her toddler son, Levi (pictured left)

However, a source who identified themselves as a prison official revealed to News9 Hilberling was found hanging in her jail cell in an apparent suicide.

Prosecutors alleged that Amber Hilberling shoved her 23-year-old husband through the window after they'd argued over splitting up.

Hilberling, who was 19 at the time and seven months pregnant with the couple's child, claimed that the death was an accident caused by 'unusually thin' windows in the couple's high-rise apartment.

During Amber Hilberling's trial in 2013, Joshua Hilberling's family testified that on the eve of his murder, the Air Force veteran had packed his bags and was planning to leave his wife after enduring abuse at her hands.

Jurors were shown a copy of an emergency protective order he had obtained against his wife a month before his death, allegedly she had thrown a lamp at his head, leaving him needing stitches.

Self-defense: Amber Hilberling, pictured left with Joshua, argued that she pushed her Air Force veteran spouse (right) after he grabbed her by the shoulders during a heated couple's quarrel

Tragic: She was seven months pregnant with a son when she killed her husband

Long way down: Mr Hilberling fell from the 25th floor of the tower and landed on a parking garage below

This image released by the Tulsa County District Court shows the interior of Amber and Josh Hilberling's apartment after the man's death in 2011

This screenshot from a video shot in 2011 shows the busted window in the Hilberlings' apartment after Joshua's fatal fall

The image above is a still photo of the broken window through which the 23-year-old veteran had fallen

A view from the couple's apartment in the high-rise building, with broken glass in the foreground

This screenshot shows a heavily pregnant Amber Hilberling being questioned by police on the evening of her husband's death

But the order was dismissed when the couple missed their court date.

Amber Hilberling had testified that on June 7, 2011, she pushed her husband in self-defense after he grabbed her by shoulders during a heated couple's quarrel, but she said that she never intended for him to fall out the 25th-floor window.

His body was found crumpled on the roof of the garage.

Amber's mother, Rhonda Whitlock, suggested at the time that her seventh-month pregnant daughter, standing at only 5 feet 5 inches tall, could not have pushed the 6-foot-6 military-trained man to his death.

'The facts just don't add up,' she told the station NewsOn6 in December 2011.

Two days after her arrest, Amber was released on $250,000 bond, but in January 2012 a judge sent her back to jail after she had repeatedly violated the conditions of her release by failing two drug tests and not charging her ankle monitoring device.

Amber had previously rejected plea deals from prosecutors and decided to take the case to trial, which concluded with a guilty verdict and a lengthy prison sentence, handed down in April 2013.

Hilberling, pictured far left, had obtained an emergency order of protection against Amber

Rocky marriage: Joshua's family testified during Amber's trial in 2013 that he had packed his bags and was planning to leave his pregnant wife. They claimed Amber had been abusive towards him

In a prison interview that aired this past February on the talk show Dr. Phil, Hilberling reiterated she was acting in self-defense.

'He reached out and grabbed me. And I was pregnant. And he didn't care,' Hilberling said on the show, according to the Tulsa World. She added: 'I pushed him off me. The window wasn't supposed to happen.'

The Oklahoma Court of Criminal Appeals upheld her conviction two years ago.

Bryan Whitlock, Amber's stepfather, told the station KTUL Monday that medical staff at the McLoud, Oklahoma, correctional facility was treating the woman's death as a suicide, but they would not say how the 25-year-old took her life.

The stepfather insisted there was 'no way' Amber, who had just celebrated her birthday on October 1, would have killed herself.

According to Whitlock, Hilberling was 'excited' about the prospect of telling her side of the story in a planned interview with KTUL, and she was also taking college courses and speaking daily to her young son, Levi.

On a Facebook page titled 'In Loving Memory of Josh Hilberling,' someone posted a status update Monday that read: 'We heard that Amber Hilberling hung herself in prison this evening. We know how it feels to lose a child. I wouldn't wish that on anyone. It's something no parent should have to experience. Condolences to those who loved her.'

A prison official reportedly claimed Amber, pictured above with Joshua Hilberling in his Air Force uniform, was found hanging in her cell

On Monday night, a man believed to be Joshua's brother, Zach, posted the messages above in reaction to Amber Hilberling's passing

Meanwhile, a message appeared on a Facebook account associated with Joshua's brother, Zach Hilberling, seemingly gloating at the news of Amber's suspected suicide.

'Muhahahahaha ding dong the witch is dead!! Muahaha,' Zach appeared to have posted in reaction to his former sister-in-law's passing.