How do I stop my sister from turning into an evangelical?

My older sister has started dating this guy who goes to an evangelical church. They have a lot of scary fundamentalist views about things and she is starting to get sucked into it. She says he forbids her from watching Will and Grace because there are gays in it, and she is starting to use a lot of weird jargon. We were raised Catholic and I am worried about her. I feel like it is almost like a cult and I am worried that she is following the wrong path. Is there a way to bring her back to reality?