Michael Miller was found shot to death Sunday morning at Wells and Douglas roads.
The Madera County Sheriff's Office initially detained 32-year-old Trisha Lynn Richardson as a person of interest in the case.
On Monday afternoon, they said she admitted to having a romantic relationship with Miller and confessed to killing him.
Richardson was arrested and booked into the Madera County jail on charges of first-degree murder and interfering with an officer.
Her bail is set at more than $1 million.