No one knows your situation the way you do. Some of the guests talked about the importance of helping hard core mormons to be open and accepting to ALL their brothers and sisters in the church, regardless of sexual orientation. Of course she won't want to watch something that in her mind attacks her religion. Even selfish at times. Sexually, risque and the such is essentially the same as baptists and fundamental Christians. I wouldn't just give up, but be wary. A shitty sex life, potentially. They will teach the girls that sex is bad and wrong, which is something they will have trouble putting behind them when they eventually do get married. If you are a Catholic girl dating a Mormon guy, then it may not be an issue with his parents. We all know people who know that the gospel is true but they will not accept it.
And no one has the right to judge you for your decision. If you are all sealed together, you will be together forever in the Celestial Kingdom. Marrying a non-Mormon is not something you do it is something that happens. It has worked and my children are very protective of their father. There is still a chance you can work out your differences, but it will require major concessions on both sides. My beliefs have changed several times in my life, but not those things, so my interfaith marriage has lasted 25 years. This is my own personal opinion. Marriage is unbelievably amazing and indescribably painful; I have been at it for 28 years with my soul mate. I had tears in my eyes and goosebumps while reading it. As a matter of fact, you can begin here.