You don't understand, I'll try another way. (What I write is purely my personal preference.)
Having sex with the sleeping nun is unacceptable to me because she did not consent to it. (Yes, she wants to have sex. Probably with the hunter. But she didn't agree to it because she's not conscious.)
If the elf knows that her mother has died, but decides that life goes on, fine. (As you wrote, it has the chemistry, it has the needs, etc.) This is her decision.
But she doesn't know the truth, or she would decide otherwise. (and she would die) So, I'm not having sex with the elf yet. I don't feel it's fair. That is why I want the opportunity to save the elf's mother. (Yes, It's your story, your game, your choice.)
Look, you're a really great developer. The art is beautiful, the writing is correct, the game is good. But even the greatest sometimes make mistakes.