(DECATUR, IL) — The 23-year-old sister of a former Centralia Marine recruiter has been sentenced to 50 years in prison after she pleaded guilty Monday to first-degree murder. Katrina Giles was facing life in prison, the same sentence her brother, Timothy R. Giles, 31, is serving after he pleaded guilty to first-degree murder and attempted first-degree murder early last year. Timothy Giles was a 27-year-old Marine recruiter stationed in Centralia, who had recently lost a custody battle with Casey Eaton over their infant daughter. According to prosecutors, Katrina Giles allegedly helped her brother plot to kill his former girlfriend Casey Eaton and her family in August 2011. Casey Eaton was seriously injured in the attack that claimed the lives of her mother Cindy and sister Lindsey. After the attack, Katrina Giles texted Timothy Giles’s girlfriend purporting to be her brother, from his cell phone, that was in her possession in Centralia, far from the murder scene. This was done to help him to establish an alibi. Katrina Giles was given credit for 1543 days served in the Macon County Jail. Authorities also say Giles must serve 100 percent of the sentence, followed by three years of supervised release. Giles, who was a 20-year-old pharmacy technician student at the time of her arrest, will be eligible for parole in 2061, when she is 70 years old.