I am in agreement that it is nothing to worry about. I was Nancy Drew and Trixie Belden obsessed as a kid, yet am very well read now. (I even finished the Proust years ago)

Sometimes I have the same worry about DD8, she did read Rainbow Fairies back when, though she hated Harry Potter this summer. But then finds something like Dear Diary she won't put down. As long as she keeps reading.