Ka Yang, who is 29, is being held without bail in Sacramento County Jail. She was arrested Tuesday, three months after her 6-week-old daughter was found dead in the family home.
Police described the child as suffering "extensive thermal injuries." Officer Laura Peck says investigators pinpointed what they believe is the cause of death by looking for other cases involving similar injuries.
They found three in the U.S., all after children were burned in a microwave: in Dayton, Ohio; Galveston, Texas; and New Kent County, Va.
Peck says police do not have a motive. No attorney was listed for Yang.