I remember when the demons were about to loose hell at the end thinking, "I bet that little girl has an angel," and yup, in about 20 seconds after I thought that she exorcised the first demon. Then when Castiel's old host called her "Castiel" my first thought was, "How does he know which angel it is?" I paid attention, and there was nothing that happened to make me think, "Oh, yeah, that angel is definitely Castiel."
It's just all very sketchy if you ask me. I think we've just seen the ol' bait and switch.
Though I was almost very disappointed to think that they would be keeping the Winchester's angel contact in a little girl's body. Whether that was Castiel or not, that actor does a damn good job portraying a scary-powerful angel. Getting a little girl to take his place would be worse than the actor switch for Ruby at the beginning of this season.