R.D.
I found a Disney Princess book (through Scholastic, I think) called 'Polite as a Princess'... it's pretty good. I bought it when my girls were 2 and 3, so I don't know if it would still be age appropriate for a 6 year old, but it may be a good start!
You might also want to mention this to her guidance counselor at school. My 6 year old, when her baby brother first came home (she's the middle child), had a really hard time adjusting. I called her guidance counselor and they met a few times and it really, REALLY HELPED!!