It has been a while since I played, but I think I do remember noticing the weaker responses to stimulation near the end of the game. A slider would make sense for the old game so you can get the first responses without resetting.
However, I think it would feel out of place with the new rank system since you can reset her rank and get stronger reactions again by getting caught which feels very natural. After all, she slowly gets desensitized by not getting caught, but once she is caught, she gets the same thrill she started with for a while.