First of all I must admit that I have not been looking at Women before marriage and after marriage so closely to know the difference. I feel now that you have pointed out I would take note of it in the future 😉
I guess more than horoscope it is the happiness of alliance and relationship that shows on the face. I know for sure being a Face reader myself that our face and expressions speak. Happiness or sadness from within shows on the face. Therefore if the girl is bright and pretty it means that she is happy while if she is grim and sad then not happy with her relationship.