Amazing project! Any plans to port this to other languages? My main language is French, and I'm looking for good old books for my daughter. She read through the Comptess of Ségur's "Les malheurs de Sophie", and she loved it.
If she's a bit technically inclined, Jules Verne is an obvious choice - though I didn't read them in French, his books absolutely fascinated me as a child.
Based on your previous choice, I suspect she's much too young for Flaubert? His writing is marvellous.
On the other hand, avoid Malot and his ilk - it's just depressing stuff.