the_rck

Possibly the Artemis Fowl books. They may be a bit too violent; people do get hurt badly in some battles against trolls and whatnot, though never for very long before they're healed. They're briskly paced and fun without being too demanding on the attention span. Perhaps some books by Zilpha Keatley Snyder, too, which have a bit of the same feel as Blume but with less overt social morals. She might like Pratchett's Tiffany Aching books, which are specifically YA, though they sometimes deal with some fairly dark themes. You'll probably want to read those first yourself to check.