I haven't done much research in this area but I know our tester was absolutely shocked when they tested our DS's reading and spelling at his assessment- mostly because they were in-sync. He said early readers (even if they learned phonics) are typically whole-word readers and rely on their excellent memories to learn to read. My son was unique because he had "habituated phonics skills."
Again, not sure what that means developmentally but it sounds as if most of the young readers and gifted kids are "out-of-sync" like your DD. FWIW, I'm a very good reader, great with grammar and writing and a horrible speller. Thank goodness for spell check!!
