It's not like Drogo has any way to be aware of such minute sensibilities, and she was not lying back and thinking of England - she actively encouraged his touch when she said yes. I haven't read that scene in years, but I recall her moving his hand to some dirty place to make her permission explicit.

And the whole issue of consent to refuse is an entirely different question in these societies. From a strictly technical PoV, Rhaegar did, in fact, rape Lyanna, because she was not in a position to lawfully or ethically give consent.