Tierra Ortega, 25, is accused of one count of assault on a child, causing death, and one count of great bodily injury, according to a statement from the San Bernardino County District Attorney's Office.
Emergency responders found 7-month-old Ezlynn Ortega suffering from skull fractures Tuesday morning at an apartment in the 600 block of North Wedgewood Avenue.
Her 1-year-old brother, Jerricho Ortega, was allegedly thrown from the two-story building by his mother. He suffered a broken foot.
A witness said Tierra Ortega jumped from a balcony after throwing her son.
Both children were airlifted to a hospital, where the girl was pronounced dead. The mother had visible facial injuries in a booking photo released by authorities.
Her scheduled arraignment in Superior Court was postponed Tuesday.
A motive in the case remains under investigation.