At the beginning of the second season the group gets attacked by a massive herd of zombies while gathering supplies from abandoned cars along a highway. During the chaos Sophia gets some unwanted attention from a couple zombies. They chase her into the forest, after which Rick follows in order to save her. After catching up he tells Sophia to stay and wait for him as he distracts and kills the zombies. During this, for some inexplicable reason, Sophia decides to do the exact opposite of what Rick said and runs away. When Rick returns she is nowhere to be found. Cue half a season's worth of futile searching only to discover she had been undead all along. It may seem unfair to target a child for making an irrational decision, but the fact remains that her running away when Rick told her to stay and wait for him got her killed. Sure, it's possible that she heard some zombies approaching and decided to leave. However, this seems unlikely given there was no evidence of this happening. It seems far more likely that her panicked state gave way to a fear of remaining stationary and alone. She probably got lost, which of course eventually led to her getting bit. Some blame could also be levied at Rick himself for leaving a clearly irrational girl alone, but it's hard to blame him given the situation. He was just trying to get the zombies away from Sophia. Nevertheless, fear doesn't condone illogical decisions, and there is no disputing that Sophia's decision to run off almost immediately after Rick told her not to was dumb. After all, it got her killed.
