
If I remember and understood it right, it (she) is some sort of malevolent force/spirit that has possessed the body of the real daughter.
Lelaians is this cult that seems to try to gather all magic for themselves for some nefarious reason. Leila would be their priestess? A leader of sorts?
That's what I gathered.

I think it's because they want us to slowly come to the realisation ourselves, in the same way Penelope has to.
In one chapter, Penelope mentioned that Yvonne was dead long ago (we saw her skeleton) and recently she noticed that Yvonne didn't even have a reflection.
But since Yvonne can brainwash people, most see her as kind and innocent. Despite evidence pointing at the contrary...
Seriously, no wonder Penelope wants to stay out of the whole situation. "Yvonne" is terrifying (⊙_⊙ )
Who is Leila/Layla??
I feel like I am missing something and reading back doesn't help ;v;