Looking for something very simple: help a guy out and come home with him to celebrate the holidays be the sacrifice for his demon/ monster-worshipping cult. What's the harm in some harmless, no strings attached fun? It's not like she's going to become the mother of horrors to bring forth the end of times.
Alternatively, an alpha wolf/ (secret dragon) shapeshifter has a really inconvenient kink: he enjoys breaking alphas and turning them into his perfect omegas.