One of my best friends is an Atheist/Christian?

we have been friends for a while now and we have always talked about the bible and stuff and she goes to the same church as I but then she was spending the night at my house and she turns on me and was like the Bible isn't true its all fake and sat there and made fun of me for being a christian but then that Night I saw her at CHURCH! she was worshiping and praying like a normal christian and i didn't wanna make a scene in church so I didn't say anything to her while there but a week after that was church camp and I told both of our other best friends and they believed me and we all sat down and talked bout it (just me and the other 2 best friends) and we all agreed that she treats us all like crap and we had enough but we didn't wanna say anything at church camp because by the time us 3 sat down it was the last day of camp and right after we got back from camp we wanted to say something to her but i had to go out of town and im out of town right now and they both want me there to do this but my question is how should we say it being a friendly christian and not be rude?