I am a big fan of Carley, and when replaying The Walking Dead and really do miss her. Gins of a well written character. Although Lily pisses me off during the story, I actually don't think she is a bad person, she is just someone who could pushed over the edge and did something nuts, something she would not normally do. I mean it is a zombie apocalypse, I KNOW I would do some things that I right now would normally do.
Personally I would love a redemption arc for Lily in Season 2, to cleanse her of her crime of killing Carley/Doug, where she will probably have to sacrifice herself.