Suceli Margarita Ardon was held Wednesday on at $100,000 bail pending a court appearance on arson and destroying evidence charges, Washoe County Jail records show.
It was not immediately clear how the baby died.
An autopsy shows the infant was dead before the body was set afire, police said.
Ardon allegedly told police her daughter, Randy, stopped breathing one night, prompting a panicked Ardon to dump the child on March 6th because she feared she would be in trouble, KOLO-TV reported Wednesday.
Ardon told police she later returned to the field to visit her daughter.
A woman walking her dogs found the body on Monday.
Randy suffered from severe congenital health problems and was considered terminal. She had a surgical opening for a feeding tube, and that helped lead investigators to Ardon, police said.