The Walking Dead - Episode 2.07 - Pretty Much Dead Already - Another Interview with Robert Kirkman

How will having to kill Sophia affect the group, particularly Rick (Andrew Lincoln)?
Robert Kirkman: This season is very much about Rick's emergence as leader or making the decision that he's not that great at it. He's torn in that everyone is looking to him for answers constantly and he is the de facto leader of this group, but it's not like he asked for this. Over the course of this season, we're seeing him making a lot of decisions and being forced into making decisions that don't end up being good ones. This situation with Sophia is a very good example of that. Leading to that girl turning into a zombie and ending up in that barn is very much a decision that he made, so it's going to wear on him. Moving into the last half of the season, he's definitely going to be dealing with his thoughts on how they got to that point, and it's going to be a tough thing for him to deal with.

Hershel and his family knew the survivors had been searching for this little girl. Did they know Sophia was in the barn? Did she wander in to take cover and fell prey to the zombies?
Kirkman: That's all going to be revealed when we come back in February. That's definitely a big question. Shane (Jon Bernthal) was pretty pissed-off and I don't think he's going to calm down after the initial shock of seeing Sophia. When we pick things up, things will be at a pretty high level of intensity and that's going to be the first question that's asked. Did they know she was in there? And if they did, why were they hiding that information from them? These groups are already very much at odds over the fact that Hershel doesn't want them to stay there, and they feel like being sent back on the road will be a death sentence, so they've already got enough to fight about and this is just one more problem being thrown into the mix.

Source: Full interview @ TV Guide