U.S. District Judge Donald Molloy sentenced Graham, 22, to 30 years in prison on Thursday, after she pleaded guilty to second-degree murder last December.
Graham confessed to being unhappy with the marriage, and pushing Johnson into a ravine after an argument.
"I just pushed... I wasn't thinking about where we were," she said.
"After providing several false statements to law enforcement officers and impeding the investigation by providing false information, Graham ultimately admitted pushing Cody from behind with both hands," prosecutors, who had asked for life in prison, said Thursday in a statement.
Graham had initially denied wrongdoing in Johnson's death, telling police that he went on a hike with his friends when he fell.
2014: The Year in Music [PHOTOS]