Nice character analysis, pretty spot-on.
I will say that with Sarah, the reason that we grow to care about her in such a short period of time is because we get to play as her. This instantly creates a connection to the character. And as we control her we get to experience her fear as she wakes up alone at night and slowly watches the situation get worse with no power to do anything about it. And it's that last bit that speaks to us all. We've all experienced moments in our childhood where some kind of tragedy struck, and all we can do is just observe it and hope the adults will make it all better, because we're at an age where we can't fully understand the sistuation. And in Sarah's case the adults in question were equally powerless.