This discussion may contain spoilers!
All we know about Carley's Pre-Apocalypse life is that her parents are Lutheran, she is a radio journalist and she came to Macon to cover the Cherry Blossom Festival. Here is my backstory for her......
Carley had an ordinary childhood, sometime, maybe about a year or two before the Apocalypse she was in a relationship with Carver(yes, the Carver from Season 2) he was extremely abusive towards her and often hit her resulting in the scar on her face from the first season. She was close with her mother and father. When the Apocalypse happened, her parents lived in California, so she couldn't get to them. She had no family or relatives in Atlanta giving her no reason to go there.
Yeah, I know the Carver thing is a little crazy but if Clem tells Carver her name is Carley he will reply with Carley hmmmmmm....that's a sweet name. He held that hmmmm for a few seconds to long and had a very creepy smile on his face when he said it. It's a crazy theory but it's possible.