I'm in the exact same pulling-out-my-hair situation that you are. Oh, yeah, and this girl belongs to a verifiable cult. I would like to compliment the brave ladies for being the strong spouse and keeping the marriage moving forward. But it is luck of the draw.
It's a great idea to know where you stand so that you'll be prepared when this comes up in conversation. It is tempting for Mormon girls to become lazy because they have such a high standard compared to typical girls. Better to now what you're going into in a relationship with a doctor or would-be-doctor. It is difficult to learn to have no expectations towards him, even though our mindset towards medicine is the same. Mixed races, however, are NOT tied into opposing beliefs and mixed races don't try to "convert" each other. If you are both in high school, she may refuse altogether. How is that gonna work.
And there is NO taking them off to wear a sleeveless shirt, cute sun dress or regular, girl-length shorts in the summer. My husband's simply daily things, like grocery shopping, cooking, waking up with me to make coffee in the morning-are far from unnoticed. Vh65, your marriage is a black swan. Anything she learned about mormonsim, she wanted to learn on her own. That was enough for him. And for mormons, the goal is always a temple marriage and a marriage for the eternities.
Even though it sounds like she is very Mormon, I feel that this will help her. But it is important to be ruthlessly honest with yourself about how you feel about it. There is a difference between commitment and time together.