Toni Fratto was interviewed by CNN's Anderson Cooper in an episode that aired Friday afternoon on his talk show, "Anderson."
"I am sorry for not saying anything and stopping him," Fratto said in her jailhouse interview.
Fratto pled guilty to helping ex-boyfriend Kody Patten kill Micaela Costanzo in March 2011. She said Patten pressured her to commit the crime.
"Kody said just do it, just do it," Fratto explained. "I was terrified. I didn't know what to do."
Costanzo was beaten to death with a shovel and her throat was slit before she was buried in the Nevada desert.
An apology from Fratto's family to the Costanzo family was not well received Costanzo's mother, Cassie, believes jealousy is behind the murder. The family still seeks answers even though Fratto is serving time befind bars.
"She has to know why," Fratto's mother said.
Fratto will be eligible for parole in 18 years.
Patten is expected to plead guilty to first-degree murder next Wednesday in an Elko courtroom.