Has she read "Walk Two Moons" and other books by Sharron Creech. While this lands in the genre of a children's book I consider it more of a pre-teen book. While the reading level isn't at all difficult the themes in the book are very appropriate for tweens.

I wouldn't write off all "teen" labeled books while a large portion of those are teen romance they are some gems to be found. Many books can be found on both 'teen' and 'adult' reading lists. If you look through the list of "Best Young Adult Books" on Goodreads you can find books that I'd list as adult and some I'd list as for kids.

What about?

Mrs. Frisby and the Rats of NIMH?
The Graveyard Book or Stardust by Neil Gaiman.
Book of a Thousand Days by Shannon Hale.
An abridged version of Pride & Prejudice.
The Call of the Wild & other books by Jack London