The White Witch is definitely NOT human. She purports to be, but even in Charn we see that Jadis's people are not quite the same as us. Lewis didn't properly integrate the information about her, but it's clear that she is NOT human, has some giant blood, and a lot of artifice that suggests she is human. (I'd like to know more about the humanoid Charnites).
In the Space Trilogy Lewis made the inhabitants of Perelandra humans, in honour of the form taken by the One who ransomed our dark planet. Yet they were not descendants of Adam and Eve. When he had the Charnites seem human, perhaps he had this in mind, that they were of the same form but not of our Race? If they are a blend of human and giant, then it wouldn't be correct to say Jadis had no human blood.
This needs its own topic. When did we last discuss it?