In fact, the church is designed to help people come unto Christ, who is the only one who can change our hearts and help us overcome ourselves to come back to him. Everyone has their own sins and impure thoughts they need to overcome.
It seems like mormons in particular are even more crazy than the majority of crazy religious people, and the manipulation and treatment of people who wish to think for themselves and challenge their beliefs is really frightening.
And if you can make it to the Tree of Life and still be with your partner, guess what. Marrying a non-Mormon is not something you do it is something that happens.
Just know that she has been indoctrinated to believe that she wont reach the highest level of heaven if she isn't married in a Mormon temple to another Mormon.
I think love and caring can be more important. One of the most well known church prophets stated that he would rather see his own child dead in their coffin than married outside the temple.