If Nahiri had been under the delusion that she was Avacyn and that delusion was dispelled why would she be referring to herself as Avacyn? The last couple of spoilers for shadows over Innistrad seem to be implying that the angels of Innistrad are turning against its people. It cpuld be that Nahiri as Avacyn controls the angels and is using them for her vengeance.
Nahiri is Avacyn