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Jordan Linn Graham, the Montana newlywed who pushed her husband of eight days to his death from a cliff, is appealing her own guilty plea and 30-year prison sentence.

In documents filed Thursday in U.S. District Court in Missoula, attorneys for Graham indicated that they believe prosecutors and U.S. District Judge Donald Molloy reneged on a plea deal in which Graham, 22, agreed to plead guilty to second-degree murder in December.

Graham's prosecution and trial were front-page news around the world last year, even landing on the cover of People magazine.

Jordan Linn Graham leaves U.S. District Court in Missoula, Mont., after a hearing in March.Arthur Mouratidis / REUTERS file

Graham unsuccessfully sought to withdraw her guilty plea after Molloy sentenced her last month to the maximum 30 years in prison even though her attorneys asked for a 10-year sentence in return for the change of plea, which came after the start of her trial.

The filing alleges that in calculating Graham's sentence, Molloy improperly added irrelevant obstruction of justice adjustments and failed to consider that her acceptance of the plea implied that she hadn't premeditated the death of Cody Johnson on July 7.

All of that adds up to "breach of the plea agreement," they charged.

Graham admitted killing Johnson — whom she'd married just eight days before — by pushing him off a 300-foot cliff in Glacier National Park.

For days afterward, she insisted that she shoved Johnson in self-defense during an argument. But prosecutors introduced evidence showing that she'd confided to a friend that she was unhappy in the brand-new marriage, had made up a false story to account for Johnson's disappearance and concocted the scenario in which she eventually led investigators to his body.

Specifics of the calculations that went into Graham's sentence weren't immediately available Thursday night, as her court presentencing report remains under seal.