What hint could she have had that a Game of Thrones spinoff MIGHT have a sex scene? There is no possible way she could have possibly known about an IP that's been absolutely gigantic for going on 10 years. What an absolute blindside. /s
Self advocating is a skill learned as a toddler, not as a full grown adult in industry being asked to do industry work. I'm saying she accepted an acting role and is complaining about being asked to act. Not that she couldn't set her own boundaries, or that she hasn't. I fervently hope she has, in fact.
However, giving yourself anxiety about maybe being asked something in the future and having to make a decision is a non-starter. Make a decision either way and stick with it. Have the confidence in yourself to make a choice. Changing your mind later is also a choice, but that one will kind of make you a bit of a bitch, and even then only for allowing yourself to be pushed around.