agree and disagree. obviously there is a script and narrative as she verbally expresses her shock at his size and reaches for a tape measure.
But I was told by a porn actress years ago that when you see a girl using their hands to subtly push the guys body back during penetration, that is a sign to the male actor to back off/ease up/too much/it hurts. She does this here, as do many women in some of these scenes with mandingo or any of the larger guys. if you watch the scenes closely, you can see them do it. THAT is not acting.