Im not too sure how in depth Miura wanted this to be in its relation to the divine, but if you've ever seen religious sculptures, try looking at just their faces. They're in utter ecstacy. I think here and what ultimately led to Casca's mental destruction was that physically she's in sexual union with a man she's loved and longed for, and at the same time not, tho she is in contact with a technical God so as a lowly being she cannot help but feel what comes with meeting a God, i.e. all the emotions, literally all of them. But her mind is destroyed because wholly the person as Casca her Ego, fully rejects this while her body cannot. It isn't a question of enjoyment or not, that shortchanges the whole arc of her character and how it's destruction here makes her one of the more complex and layered individuals even as a mental vegetable.

idk it just felt like she enjoyed it anyway fuck casca should of died by now smh