Johnson's body was found at the bottom of the cliff three days after he was reported missing by a friend and co-worker. Graham said at her trial that she was having second thoughts about being married so young and they went to the park to talk about it.
They argued heatedly at the edge of a steep cliff. Johnson grabbed her, she became angry and she "just pushed" without thinking about where they were, Graham said then.
She didn't tell anybody what had happened, instead making up a story that Johnson had gone for a "joyride" with friends from Washington state.
That story unraveled when the versions she told to friends, relatives and authorities didn't match.
In court filings Tuesday, Assistant U.S. Attorney Zeno Baucus asked Molloy to impose a life sentence or else no less than 50 years in prison.
Graham showed no remorse, left Johnson's mother without a child, upended a community and had no respect for the law in the process, Baucus argued.
"Through her actions, including the murder of Cody and conduct that followed, the defendant has demonstrated that she is extremely dangerous, predatory and an unrepentant murderer," he wrote.
Federal public defender Michael Donahoe said in his recommendation for a 10-year sentence that Graham ultimately accepted responsibility and is sorry she didn't come forward sooner.
She did not obstruct the investigation, and her fabrication of an email designed to support her story that Johnson had driven away was "the emerging cry of defendant's conscience," Donahoe said, noting that Graham was the one who led authorities to Johnson's body.
If Graham "was a cold-blooded killer, she could have left Mr. Johnson at the bottom of that ravine. He would have likely never been found," Donahoe wrote.