I know other such people, even much worse examples. The thing is that the one I'm talking about was not like that in the past, over time she has become wolfish, so to speak, in the figurative sense of the word. For blood, again in the figurative sense of the word. Or perhaps this remained the most suitable means of survival for her.
An acquaintance of mine called her a "monster", but yes, energy vampire is the most appropriate description.