How is it that you guys have been friends for more than 10 years yet she doesn't know you don't believe in God? I'm surprised it hasn't ever come up with you going to her church and all. Also, I think it's great that you respect her religious views and still attend church with her and her family. Obviously you must enjoy the experience somewhat to attend despite your beliefs. I think you will just have to be honest with your friend. They are under the impression that you do believe. If her reaction is negative, then she isn't a real friend. Hopefully she gives you the same respect you give her.