The feelings she is talking about comes from the cult mind-control. All JW's believe that is we go against the "rules" not dating a nonjw that God will kill us. I know it's hard to understand but it all comes down to fear. I have only recently broke free of the JW's and this so far has been the hardest thing I've had to do in my life.
I truly am sorry for you and the pain you are going through, but this girl is deep in the cult and it's very hard to break away because if you do...you lose your whole life in that you lose your family...they think of you as dead, and you lose ALL of your friends. The JW's control by using fear. Fear of God and fear of losing your friends and family...
Ask anyone on here, it's happened to all of us that we lost someone when we left. My Aunt, cousin and my grandmother all refuse to talk to me and they think I'm scum and God is going to kill me because I left. If she leaves the JW's, that is probably what she is fearing. Fear of God and of losing her family.
It's hard I really do feel for you, but read the book the other person told you Crisis of Conscience...Also if you want to understand the mentality behind cults and mind control, Read some of Steven Hassan's books.
I know it doesn't make sense to you, but you are not fighting her, you are having to fight the cult mentality she has been indocternated with probably her whole life. The the JW's have a strong control over all of the members, and it's very hard to break free of it. I've been out 3 months and I'm still having to fight the pull back to the cult.
I'm not sure if this helped, but the best thing you can do is try to understand the fear and control. I was the good little JW girl, and I knew this man who wasn't a JW and he was very kind to me and I liked him a lot, but the JW in me at the time won out and I never gave him the time of day. My husband has told me about the problems he had when he was in highschool dating a nonjw and when his parents found out, they forced him to break up with the girl and he is still bothered by how me treated her. He didn't give her a reason as to why he broke up with her either. And he left her heart broken.
Peace be with you!