I need to re-read CON especially LWW & MN....
Is the reference to "Giants Blood" actually made in MN by Jadis? or is it as I suspect a statement made by Mrs Beaver?
But whichever makes the comment, it would still probably be propaganda in one form or another.. An attempt to be intimidating by Jadis, and an attempt to be derogatory by Mrs Beaver.
Personally I would take the view that the inhabitants of Charn are actually Human descended (as per my heresy) BUT thats just my own view.
As to the character of the sister of Jadis, well we only have the word of Jadis as to what she was like.
Again its just part of my Grand Heresy, but I prefer to take the view that the sister was actually honourable and was fighting to try to save Charn. (I could expand on that, but I've already done so in my Grand Heresies.. so I won't)