A custody hearing was scheduled this month for the girl's birth mother to try to reclaim her child, said Crandall Heard, the attorney representing the girl's mother.
"There was a hearing set up in the next few weeks to see if this child could go back home, but obviously that will be too late," Mr. Heard said Wednesday.
Jackson County sheriff's deputies and emergency medical personnel responded to a 911 call made from a home on Georgia Highway 334 near Nicholson about 5 p.m. Tuesday and found the child unresponsive, Chief Deputy David Cochran said.
The foster mother, 29-year-old Sharon Osborne, of Nicholson, told sheriff's investigators that she came home from a doctor's appointment shortly before 3 p.m., unloaded two adopted 3-year-old girls from the van and went inside.
Once inside, Ms. Osborne lay down for a nap, and she forgot about the baby in the car, Chief Deputy Cochran said.
She woke up about 5 p.m. and rushed out to find the girl unresponsive in her car seat.
Ms. Osborne's doctor had prescribed medication that might have contributed to her disorientation and drowsiness, Chief Deputy Cochran said.
Sheriff's investigators have sent the girl's body to the Georgia Bureau of Investigation Crime Lab in Decatur for an autopsy, but Chief Deputy Cochran believes the girl died from a heat-related illness. The temperature in the Athens area reached a high of about 86 degrees shortly before 4 p.m. Tuesday, according to the National Weather Service.
The baby had no known medical problems, Chief Deputy Cochran said.
Sheriff's detectives will talk with prosecutors to decide whether to charge Ms. Osborne with a crime.