I was like that growing up. I'd read the cereal package over and over just to have something to read at breakfast.
Heck, I'm still like that when time allows -- nothing beats starting a novel at 9 pm and finishing it at 2 am or whatever.
DD3.9 is like that -- we typically read 15 books (plus about that many online stories) every week. Of course, they're not 4th grade RL, but I can see her doing something like that when she's 7.
I remember for decades, going to a bookstore was PAINFUL to me (we didn't have public libraries where I grew up...
) because of the sheer POSSIBILITY of it all -- how much there was to learn, to experience, to ponder.
I think that level of voracity is a good thing. It will serve her well -- as long as she doesn't neglect other aspects of her life. If you want to see what happens if she has more reading time (ie, if something satisfies her, or if -- quite possibly-- nothing is "ever enough"), you might want to make sure it's dispersed throughout the day.
