Farfanara, you are correct when you say that when intoxicated it is sometimes not possible to scream "No".
That said: no is a very easy monosyllabic word to say. If you don't while you can throw out cohesive questions like "It hurts. Baby, why are you doing this to me?" then "no" or "stop" are definitely within the mental range. The reason she didn't do it is psychological, not chemical.
The guy wasn't paying enough attention to her feelings, when you are caught up in sex and especially if intoxicated it's difficult to read between the lines, especially from someone mumbling into their pillow from 2-3feet facing away from you.