That sounds like at least a very fun and educational exercise, trying to adapt into a screenplay a novel that just doesn't want to be adapted. Like, if nothing ever comes of it, you will still have built some Skillz! I'm sure Lewis is proud of you for that!

Sadly, Sophie herself doesn't actually APPEAR in my finished fic, but I have written a bit of her interacting with Chrestomanci in the crossover draft and that's fun. :) Someday, it will be a proper story!