Dawn to be honest, from the transcripts mind you as Season 6 has not screened in Oz yet, is a bit of a dual character.
In the opening episodes, we see her come to terms with the loss of Buffy and her Mom and then deal with the shock return of Buffy. She does this maturely and by all accounts it's portrayed well. She seemed to be looking out for Buffy and we had an apparent role reversal. Buffy being protected by Dawn.
Lateley however the story line has Dawn being a pain in the rear.
It's a bit of a contrast and not explained very well. Granted she is behaving exactly like a troubled teenager, but I expected her to be different given the nature of how she came to be and what it took to protect her.
My humble opinion.