posted 10-05-2000 07:23 PM
As far as I can reconstruct, the Anya mythos is as follows:"Previously, not on Buffy" : Anya was a normal girl, not necessarily looking as she does currently. She went through a similar experience to Willow, and D'Hoffryn granted her the vengeance demon aspect.
"Buffy Season 3: The Wish" : Anya appears as a schoolgirl, in order to exact revenge on Xander for Cordelia. It's not clear if this was her true form or not, but one would have to think NOT, since she's appeared to all manner of women over the ages. The spell is broken - ie, the amulet from which she derived power smashed - and she retains her current form.
"Buffy Season 3: Later" - Anya remains a schoolgirl, and begins to act more and more like one. She retains knowledge of her hundreds of years of past, though. {Grad 1/2}
"Buffy Season 4: Up to.." - Anya seems to remain an ordinary girl, although without the social skills thereof. She also seems to have a brash attitude to demons and danger that we all assume is due to that lack of skills.
"Buffy Season 4: Wild Things" - Anya gets a spike through the hand, and keeps going. What the??
It seems clear to me that there is some vestigial aspect of the demon in Anya that hasn't been fully explored. Perhaps she retains her demonic healing powers {those which cause her to live forever etc}, without the actual magical ability to exact vengeance. It would appear that she has a level of magical ability in herself though, somewhere above Willow, but below the rather scary Tara.
Then again, magical ability and strength of spells actually cast isn't a good indicator of internal magical ability {Becoming 2, The Zeppo} - merely that they can read. Ease of spellcasting would seem to be it...