Ka Yang, 30, faces murder and torture charges. Prosecutors said her lack of a criminal background deterred them from pursuing the death penalty.
Yang was not arrested for the crime until June 21.
It took several months for investigators to determine the child's burns came come from a microwave using medical analysis and findings from three other U.S. cases.
Yang told police she suffered a seizure while holding her daughter, and woke up with the girl on the ground next to her.
However, an autopsy determined the infant died of "extensive second-, third- and fourth-degree thermal injuries."
Child welfare workers removed Yang's three boys, who are all under age 7, from her home.
Yang was pregnant when her baby was found dead but did not know it.
Sacramento police said they do not know what would have led Yang to allegedly put her baby in the microwave.
Friends told FOX40 Yang always wanted a girl and waited years to have one.
Yang is being held without bail.
Her family says they are worried about her health in jail.
Yang is prone to seizures, and has been having more since she's been in jail, her mother told FOX40.