[susan53]

It's awkward, as she's on the fringe between primary and secondary, but if you want something intellectually challenging, go fo secondary - especially if she's nearer 12 than 10.
Have a look at the CUP secondary catalogue. I don't teach that age group myself, but they're the sort of books I'd go for if I did, Some of the authors are known for including cognitive development in their work as well as "just" language learning (eg Herbert Puchta) while personally I like other things written by Ben Goldstein very much.