Un Young Lee was booked at the Walnut Sheriff's Station and was being held in lieu of $1 million bail.
Lee was detained Wednesday as a person of interest in the death of her 77-year-old mother-in-law, Young Ja Lee, and was suspected of setting the woman's Diamond Bar house on fire.
Los Angeles County firefighters responded to the fire in the 1200 block of North Diamond Bar Boulevard around 1 a.m. After a preliminary search, the cause of the fire could not be determined and no one was found inside.
Authorities then received a tip that Lee may have killed her mother-in-law and set the house on fire. The anonymous tip also identified Lee's white minivan. Authorities found her sitting in the car at Tustin Ranch Road and Greenway Drive.
The car was filled with many bags, authorities said, and they believe the victim's human remains were inside them. The van was towed and taken to the Orange County Coroner's office for further examination.
The investigation is ongoing.
Lee is scheduled to appear in court at the Los Angeles County Pomona Municipal Court on Friday.
Anyone with information about the incident is asked to contact the Los Angeles County Sheriff's Department's Homicide Bureau at (323) 890-5500. Those who wish to remain anonymous may call "Crime Stoppers" at (800) 222-8477 or texting TIPLA to 274637.