My DS5 is sort of over all his lovely picture books, though I'll find him poring through them if we've been too long between library runs. There are certainly some sophisticated picture books out there, but if that no longer appeals, I think that's okay. Do you really feel she has oodles of her own books to choose from? Even with a great in-house selection, nothing beats a shiny load of new library books with enticing covers over here. Both of my kids usually have 30+ out at a time. Mind you, in DD's case, she often does not read them all before we go back, but that's okay. It's the smorgasbord concept.
Both of my kids really like nonfiction too...but if she loved Harry POtter, etc, she doesn't sound like she is one of those who just isn't into fictional worlds. Dare I suggest that your own confessed fussiness might be subconsciously limiting what you offer her? Do you ever just turn her loose in the stacks?
