Well, I'm behind on the comics (waiting for seven to arrive), but I'm going with it being the real Fred. Sort of them both inhabiting the same body, theory.

I'm thinking that when the push to Hell happened Illyria and Fred were mixed together like paint, sort of a red + white = pink kind of deal. When Spike finds her in 6 (first night pt1) she's alone, scared and surrounded by that nice little circle but as soon as the need to protect and fight comes into play that portion of her personality emerges. She's locked up and in a rage as Illyria because she can't deal with the emotions from the Fred half of her which is in grief. When she sees Wes, it's a shock to her system and the part that desires to be with him most emerges. I'm just hoping that she isn't chared/impaled/beheaded while she is in Fred form all swoony over Wes being there. That would not be of the good.