Responses
My guess is that she's the demon queen still, but that she tossed the necklace out of grief and this asswipe stole it for his bodymod purposes cause it had some of her (or mc's) mana left over in it too experiment with. Hence the feedback he got from it initially and the appearance and bits of personality influence from it. And once he defeats it, it'll dissapate into pure mana instead of a body... That's my theory at least.
I thought the current demon queen is his daughter, such a plot twist how his daughter become like that huhu ┗( T﹏T )┛