When I was younger, I was a devoted christian. Having a christian faith and also a boyfriend was very hard for me. My boyfriend and I wouldn't have sex but we'd get close to having sex when we were intimate with each other. Because of my faith I felt so bad and guilty afterwards. I felt like I had failed my God and failed myself. My boyfriend wasn't a christian and didn't understand why I felt like this when I did. To solve this, I told him I didn't want to be put in a situation where I felt my physical side could overpower me into doing something I'd feel guilty about. Don't get me wrong, there isn't anything bad about sex. My beliefs just prevented me from doing so before marriage. So we stopped being alone together and controlled our physical contact with each other. We still kissed and hugged each other, its when we pushed it far enough we'd stop.
The best way for you to help her is talk to her. Ask her if she wants to stop doing anything sexual with her. Whether its petting or necking. Avoid places and situations where its easier to do initate things. As far as talking to her and convincing her that she isn't a disappointment to her parents, you can't really convince her because her mind is probably set on sex being taboo.You just have to give her time and respect her by not initating sex or sexual contact and if you love her, you'll do just that. Thats the best way to help her, she'll come around when she's ready and comfortable.
Hope this helps