Investigators say 68-year-old Irma Quiroz and 67-year-old Alejandro Quiroz were fatally shot during an August 2009 backyard cookout.
Carsner earlier lost custody of her then-8-year-old daughter after the couple complained to Child Protective Services that she allegedly neglected the girl.
Psychologists testified for the defense that Carsner had a history of mental illness and alcohol addiction.