I hadn't realized there's a whole genre of Susan Pevensie fanfic.
Here's one I just came across: “Between,” by genarti, about the difficulty Susan has on returning from Narnia. Sad and well done.
And I'm not up to reading “On This Side of the Door” by Transposable_Element yet, but the little I've read of it so far looks good. (It's Susan and her uncle going to identify bodies at the train station.)