I'm not going to go into detail on her skill when it comes to a gun, although that was a pretty good factor that I know made a lot of us take a second glance at her. That's obvious and I don't think anyone will disagree this point.
I liked her relationship with Lee. Not in a "I'm a horny teenager that wants to see sexual stuff" way, but it was sweet. Those two would have clicked perfectly. They would make a good team; I could see them always taking down zombies together and having each other's backs. :]
Carley was pretty, and I do admit looks can either make me more fond of a character or dislike them more. I'm a straight girly, and if I ever get stuck in the apocalypse, I'd like to look as nice as she managed to.
She was also reasonable. I agreed with her on almost everything she had to say/do. She didn't lose her temper and force herself too far into the spotlight (apart from the time it cost her her life) or hide in the shadows. She didn't get involved when it wasn't necessary. She dropped the subject and didn't bring it up again when Lee voiced his annoyance at her asking what happened in the meat locker at the St. John's farm.
She had a good sense of humor, too. She made me laugh multiple times. How can you not love somebody with such a cute and light personality? Even in the midst of fighting Walkers, she didn't shut down. She managed to keep things amusing.