Like everyone else, I think you should tell her before the wedding. I can't say how I would have reacted if I had found out down the road but I think I would have been more upset about the fact that I was kept in the dark. How would you feel if she was hiding some big secret from you? I would think you have a better chance at being accepted if you tell her outright instead of her coming home early one day to find you in a dress ya know?