I don't understand it, either, because Susan is an excellent person to have along on a quest. She will make sure you have all the correct supplies in the correct amounts, she can hunt game for extra food, she's good at dealing diplomatically with any strangers you meet on the road, plus I bet she knows a lot of stories, since she was the one looking after Edmund and Lucy when they were very small. Practicality is a virtue, not a sin, no matter what Lewis insinuates about it being associated with witches!

Sisters are the best. Brothers are good too, but there should always be more stories about sisters. :-)

...I have far too many projects in the air right now, but I will sit on this idea and see if it grows into a proper fic in the spring.