Well I have a feeling that she's the daughter of the grand sorceress. Maybe when she gave birth to Cecile she found out that she had the ethi- something blood and asked the spirit of how to remove it. At that time Cecile would have been 1year old or so and maybe she was sent to the castle and her mother fell asleep . Because it wouldn't make sense if the grand sorceress was Cecile because cecile is 24 years old and the grand sorcereress asked the spirit 24 years ago. But who knows just my thoughts
There's also the possibility that she herself is the sorceress... She lost her memories after getting rid of the blood and those time having amnesia, she considered her age to be 24. How would she be able to survive alone as a baby? She never had a single maid... Tho, it would be creepy if she's a hundred yrs old....
It could also be that during those 24 yrs, she was asleep the whole time and dreamt all the things she remembered that had happened but it can be discarded since those guards who investigated found traces of things used by a single person...
So, the FL is the grand sorceress who maybe the last descendant of Eugindiph which the ML drunk (her blood, acquiring it after many trials or some situations, i dunno, just imagine it) to gain power but she wants to return to being human after some circumstances and the side effects was her losing her memory & being found by that kingdom or maybe she wasn't part of it entirely and used some spell to hypnotize people and affected herself too (those maids that never existed) and the reason she can negate the aftereffects of the blood in the emperor....
There's also the hint of her reading the magic book which could very well hers from the start and taming the dragon...