The Orlando (Fla.) Sentinel reported Amanda Brumfield, 29, was charged Wednesday with allegedly killing 1-year-old Olivia Garcia, a girl she was babysitting in Ocoee, Fla., last year.
In addition to the first-degree murder allegation, Brumfield was also charged with aggravated child abuse and aggravated manslaughter of a child.
She reportedly is being held without bail at the Orange County Jail.
Police have said Brumfield told them Olivia fell out of a playpen. However, an autopsy completed in March suggested the toddler's fractured skull and bleeding brain were not consistent with injuries typically sustained in a 28-inch fall, the newspaper said.
The Sentinel said prosecutors haven't publicly suggested what they think happened or offered a motive.
Brumfield's mother, Melissa Parish, told TMZ earlier this month Brumfield is devastated by the death of her best friend's daughter. Parish also told the Web site her daughter had "no reason" to call 911 when the baby fell because there were "no signs of distress."
"When you have a situation that does not indicate distress ... there are no signs of distress, then there is no reason to immediately call police," Parish told TMZ, adding Brumfield fell asleep with the child after she fell, then awoke hours later to find the infant unresponsive and called for help.