Hypothesis: She won't make it.
I think Sarah won't make it very far into the game. Perhaps enough to estabilish a friendship with her, but that's about it. Considering the facts that she was sheltered since possibly the day the apocalypse began, she doesn't know anything about walkers, what is it, what are it's intentions and how to deal with it. Which might result in a scenario where she'll be left alone and attacked by a walker, completely stumped on what to do, and most likely very scared.
It just seems so arbitrary that she'll survive for so long, because i doubt she can just remain in her house for all her lifetime, and then suddenly she comes out and all this information gets poured on her, with the world gone to hell and mosters roaming the earth. Carlos needs to tell her the truth and teach her how not to die, before it's too late. Like Chuck said, it doesn't matter if you're a little girl, the only thing important in a world like this is to survive, and Sarah can't be hiding behind her dad all the time and hope she'll be saved.
Thoughts?