My take on Laurie is that she "wished" her fetus away, and the realization of that sent her over the edge. I can imagine if I were in her shoes I'd be not only wracked by the guilt but I'd also worry about the other people I love. After all if I can wish one away, why not others? So perhaps her leaving her family was her way (in her mind) of protecting them? I know she could have just left, instead of joining the GR, but perhaps we'll see more about what went into that decision in the next season.
