But I've been thinking that Susan sees it almost the same way, except as wondering why Aslan would punish her family. Because he told them all to leave Narnia and grow close to their own world...why would Aslan punish all of them with a train crash just for holding onto memories?

I think that is a really really interesting reading of it! I guess it goes against the text a little because Lewis clearly wants us to think that Narnia is the happy ending (but then since when do we care what the author intended?), but it's always *always* bothered me that--after the Professor tells them not to talk about Narnia too much and Aslan tells them to get closer to England--it's only Susan who seems to try to move on. Do the rest of them even have friends outside of their little group? Lucy, maybe, but then we find out she was a False Friend.