I feel uncomfortable when I'm with my religious friend...?

I have a friend who is a devout Christian. She doesn't necessarily try to spread it, but whenever the topic comes up, she gets really serious and antisocial. I mean, I can understand belonging to a certain religion, but i feel like you should still be open to other ideas. Personally, I really appreciate and follow some of the morals and philosophies in the Bible. I just don't think it's healthy to be so rigid in terms of beliefs. Anyways, it just really bothers me, but I know that if I confront it with her, she'll just think of it as an insult. So what should I do? Thanks! Oh, and by the way, please don't try to 'preach' to me. I already know my beliefs and I don't need anyone to tell them to me. Thanks!