She was jaywalking, apparently. The bus dropped her off directly opposite her home, and instead of walking down the road to an intersection, then back, she crossed right there, like everyone else.
That put her in violation of Georgia § 40-6-92 "Crossing roadway elsewhere than at crosswalk". It's a part of Title 40, Motor Vehicles and Traffic, even though it applies to pedestrians.
Now § 40-6-393 "Homicide by vehicle", subsection (c), defines homicide by vehicle in the second degree as any violation of any rule in Title 40 (with a few exceptions that don't apply here) that unintentionally causes a death.
The jury believed that her jaywalking led to the death of her child. And that meets the requirements of the law against homicide by vehicle. A more sensible law might have exempted pedestrian behavior, but Georgia's doesn't.