I've always just let my kids read what they want to read. They've gone through phases of repetitive, low-challenge reading and then taken sudden leaps into more challenging fare. If your dd enjoys stuff like Narnia, but lacks the stamina, you could alternate reading chapters aloud to her with independent reading. Non-fiction, anthologies of short stories, magazines and more 'mature' picture books could also easily challenge her reading without needing huge amounts of focus and stamina. But really, I wouldn't worry. My then-5yo read the first few chapters of the first Harry Potter a year and a half ago and then stalled. She didn't seem concerned -- she happily read plenty of less challenging stuff in the meantime. Then a few months ago she picked it up and read it cover to cover in a week, and has since read her way through the six remaining books in the series. She's had no reading instruction and total free rein over choosing her reading material. My three older kids progressed similarly with nothing more than self-managed independent reading.
Editing to add some specific suggestions. "The Worry Stone," "The Quilt-Maker's Gift," "Mellisande," and "Stickeen" are examples of the types of picture books I'm thinking of. Non-fiction by DK and Usborne, like this one, has always been popular here. Anthologies like "D'Aulaire's Book of Greek Myths" and "The Illustrated Book of Fairy Tales" are lovely. For magazines we're particularly fond of those in the Cricket family. Muse, Cricket or Odyssey might be good choices for a kid like yours.
Miranda
Editing to add some specific suggestions. "The Worry Stone," "The Quilt-Maker's Gift," "Mellisande," and "Stickeen" are examples of the types of picture books I'm thinking of. Non-fiction by DK and Usborne, like this one, has always been popular here. Anthologies like "D'Aulaire's Book of Greek Myths" and "The Illustrated Book of Fairy Tales" are lovely. For magazines we're particularly fond of those in the Cricket family. Muse, Cricket or Odyssey might be good choices for a kid like yours.
Miranda