Fantasy is a genre that lends itself to picking up tone, style, and world building and such from the first few pages. I'll suggest a few classic fantasy series that could stay for a long time if she enjoys them. But these are towads the adult side of young adult in terms of reading level.

These are both in fantasy humor:
Piers Anthony's Xanth series (first book - A Spell for Chameleon)
Terry Pratchett's Discworld series (first book - The Colour of Magic)

Not humor:
Ursula Le Guin's Earthsea books (first - A Wizard of Earthsea)
Phillip Pullman - Golden Compass