Dorothy Maraglino, 36, was arrested last week, nearly a month after the body of 22-year-old Brittany Killgore was discovered near Lake Skinner. Her bail has been set at $3 million.
The district attorney says Maraglino was the girlfriend of 45-year-old Marine Staff Sgt. Louis Perez, who is married to another woman. Perez has also been arrested, along with 25-year-old Jessica Lynn Lopez. All three suspects lived in a Fallbrook home where Killgore was allegedly killed.
Killgore's body was found nearly a month ago. She was last seen April 13, three days after she filed for divorce from Lance Cpl. Cory Killgore, who was serving in Afghanistan at the time.
Investigators found Killgore's blood and a weapon in Perez's car, according to prosecutors. Authorities have not disclosed a motive for the killing.
The Associated Press contributed to this report.