Could there be a deep hidden problem in your wife's past, that she has been unable to bring up.
Maybe an unwanted sexual encounter with someone she trusted as a young child.
It may be hidden so deep that she may not even remember it.
Then there are alot of women who just are not interested in sex, but they know it comes with territory, when they get married.
Also sounds to me that your marriage is more of a business arrangement then anything else.
I realize that you are in business. You both seem to like spending time with each other. Sometimes too much togetherness can create alot of friction in a marriage. Even though it does seem to be working for you in a positive way. Just remember you can't always have what you want. Marriage is a 2 way street and sometimes you do have to give up things that you feel are important you, but not important to your partner.
Sounds to me like she may find the whole act disgusting or maybe she was brought up to believe that sex was a dirty act and was only meant to bear children.
You have also got to take these things as well into consideration.
Twelve is along time to be in a marriage these days, and sometimes we have to make decisions that can affect the rest of our lives. Whether they be negative or positive.
Sometimes you may have to hurt the ones you love the most.
This may end up being an ultimatum.
Sorry to go on so much.
Good luck in whatever decision may decide on.