Authorities said Kalberg was watching Caitlyn Jolley Friday morning at her home in Eastvale. At some point the toddler suffered a severe head injury and was taken to a local medical center.
Investigators said they arrested Kalberg on Saturday after examining the nature of the child's injuries.
Jolley was later transferred to Loma Linda University Medical Center after doctors decided she needed specialized care. The toddler died at the hospital on Tuesday.
"Ms. Kalberg was the day-care provider for the young child. She was a friend of the family and had been taking care of the child since January of this year," said Sgt. Joe Borja of the Riverside County Sheriff's Department. "She was supposed to be taking care of this child but she in fact caused injury,"
Kalberg is scheduled to be arraigned on May 17. She is being held in lieu of $1 million bail.