Lopez, 25, pleaded not guilty at her arraignment Thursday, where bail was set at $3 million, district attorney's office spokesman Steve Walker said. The investigation remains open and further charges could be filed, Walker told CNN.
Killgore -- whose body was found Tuesday near Lake Skinner -- had been on a date with Marine Staff Sgt. Luis Ray Perez, 45, when she was last seen alive April 13, investigators said. Perez was charged this week, and has pleaded not guilty, to two unrelated felonies -- receiving stolen property and possession of an assault weapon.
The San Diego County Sheriff's Department previously said Perez was being "actively investigated" concerning Killgore's death.
"We believe he knows more than what he initially told us," Sheriff's Capt. Duncan Fraser said. "We do not believe he is being cooperative with us."
Lopez was arrested Tuesday at a San Diego motel and treated at a hospital for what authorities called self-inflicted lacerations, before being jailed. Investigators said they found an apparent suicide note in Lopez's room, in which she allegedly told what happened to Killgore and where her body was.