Honestly, though the end of the chap doesn't seem to be going that way, I feel like this part of the chapter gives them the potential "out" needed. If the dark elves are interested in brainwashing techniques but haven't really started any, he could disguise his interactions with her as under the effects of brainwashing magic.I also think trying to save her would be useless, he doesn't have enough power to justify reasons for releasing her and if she 'escapes' that would also cause problems for his end goal. Giving her death is the only way to save her even if its sad
Thanks for the TL