There are kinks where someone can be willing to indulge their partner for a bit because it makes them happy, and there are kinks those people just will not do. This is not an *uncommon* kink as far as I’m aware, but it is definitely one with an extremely high squick rate for people not into it (and I will admit to being really not into it either). It was fine for your GF to bring it up as something she would want to try. It is even fine for her to be upset that you don’t want to (within reason, of course). But it is not fine for her to seemingly be trying to guilt you into this. You are allowed to have hard boundaries for what you will and won’t try out for her. Maybe you could talk about it, work out what about the fantasy she enjoys, and see if there is another way you can do that that doesn’t make you uncomfortable?

She can remain asleep when you **** her? That's not a great way to market yourself. You may want to look into hip movement -- the ladies find that exciting.

Tell her to stop or you'll leave for good.

Sounds like she's an A.N. Roquelaire (Anne Rice) fan

This could be a trap to try to charge you with rape or extort money from you. Yes, some evil people seriously do this crap. Don't walk, RUN.