I touched on the "Lillith" concept in my previous heresies.
One must remember that the "origins of Jadis" are hidden in the depths of Time to the Narnians of LWW.
Their mythologies would have arisin mainly from the knowledge of Earth Mythologies and Biblical Teachings of the Pios King Frank and his Wife (sorry can never remember her name.. have a mental block there)
My original postulate was that the descent from Lillith would be used as a term of derision by the Loyal (Underground) Narnians.
As to be being the last oif the Royal House. That isn't necessarily so. As I "extrapolated" as a way of explaining the precence of three people of "fairy blood" one of whom was the "great(-ish) Aunt of Uncle Andrew.
If you wish to have your mind blown away by the Grand Unified Heresies of Erekose.. there is a (somewhat untidy, as it is sourced from the older forum which had threaded discussions which lent itself to this sort of thing better), located .. here --->
There are also a couple of additional Heresies doddted around the Chronicles forum too (such as The Great Train Accident)