Yes, its not unusual -- I think the figure of X days for a given species is kind of a best case scenario -- the most vigorous hatch out on day X, the rest take an extra day or two.
You would really only know for sure by candling the eggs, but I wouldn't want to disturb her at this point. I hope she does well -- there is another thread on here with photos of the poults from a first-time mother. Unfortunately, I let one of mine sit on a clutch of eggs, and she didn't do well at all. She had about 14 total, but only had 4 or 5 of them actually up where she was keeping warm. The rest were buried down in the deep litter underneath. The ones she was trying to incubate were all just rotten stink bombs, and the ones buried were not even starting to develop. I felt bad about taking them from her, but I put the undeveloped ones in the incubator and they are now developing, have about 9-10 days to go.
