Are you Christian also? If not, that may be why she is shunning you. In my experience, Christians, born-again and otherwise, often will not be close friends with someone who is not also Christian or even the same denomination of Christianity. Perhaps she thinks that she needs to exclude all non-Christians from her life in order to live righteously. Dunno. Religious people are weird.

Yeah, very confusing! I'm sorry to hear she's treating you this way. Losing a friend is hard, especially when you have no idea why they're gone. Been there myself. I doubt that other Christian folks don't want you around -- just her. Maybe she felt like she was cheating on her boyfriend by being friends with you? I know that's a stretch, but people can get unrealistic notions in their heads.