Brittany Dawn Killgore was last seen April 13, three days after she filed for divorce from her husband, Lance Cpl. Cory Killgore. Her body was found in brush near Lake Skinner on April 17. It's still unclear how she died.
Dorothy Grace Marie Maraglino was arrested Thursday night. Investigators haven't said how she's connected to the case. They only said she was arrested as a result of information and evidence obtained during the ongoing investigation.
Two other suspects - Louis Ray Perez, a Marine staff sergeant, and Jessica Lynn Lopez - pleaded not guilty to Killgore's murder.
Prosecutors said Killgore apparently met Perez for a night out after she filed for divorce, but things quickly went wrong. Authorities said Killgore's body was found hours after paramedics were called to a San Diego motel and found Lopez with self-inflicted cuts and a suicide note. The prosecutor said Lopez and Perez once lived together but didn't indicate when or where.
Killgore's husband has not been named a suspect or person of interest in her death.
The Associated Press contributed to this report.