Still no joy: there were a couple of times I just used the "hit her until she's dead" approach but unfortunately relying on the weapon's frost damage to stun her is much too unreliable so at some point she'll just side-step me, outrun me and as soon as she gets to complete her chain of spells it's pretty much game over: I find her utterly unassailable from that point onwards.
I did eventually succeed by resorting to cheating, but I'm not particularly happy about that. I am utterly useless at boss fights though and as a rule I hate them, so I guess I can now revert my sword back to its previous attributes and continue (as an aside, I noticed that the one-handed sword seemed to have a much better success of striking than my usual two-hander: I guess it's faster).
Still, it wasn't as bad an experience as DKS' notorious Zeppelin escort mission. D:
