God does indeed love her, He doesn’t love her sin. Its like if someone has a sickness like cancer, we don’t stop loving because of the cancer, we should love more because of the cancer, but we will still hate the cancer. It like sin can kill her. However that being said, we are all called to live chastly, whether married, single or religious. To engage in sex outside of marriage is a grave sin that can push God away from her.
She says that she is getting married, Jesus says that marriage is between only a man and a woman. What she is then in fact doing is living in a lie.Truth is not a matter of opinion. Jesus said I am the Truth, so if she has a problem with it, it is with Jesus, not you. It won’t be you that she is mad at , it will be the Lord, although you may go through a sort of marterdom for a bit until she figures it out.
The Church defines love as desiring the highest and the best for the sake of the beloved, tell her that you want the highest and best things for her, for her to go to heaven.