I'm grateful you are concerned about your friend's spiritual condition, because even if she denies it, she needs the forgiveness and new life that only Christ can give to her. Never forget Jesus' words: "For the Son of man came to seek and to save what was lost" (Luke 19:10).
It would be interesting to know why she is so opposed to God and someday you might ask her. Her reason could be almost anything, from an oppressive childhood to the conviction that all Christians are hypocrites. Do whatever you can to answer her questions or objections (without getting into an argument) but realize too that whatever she tells you may only be part of the story. Her deeper reason may simply be that she wants to run her own life and doesn't want God to interfere with her plans.
That is why the most important thing you can do is to pray for her. Only God can open her heart; only He can convict her of her sins and convince her of the truth of the Gospel. You are not working with her by accident; God put you there to be His witness.
In addition, ask God to help you be a witness to Christ by the way you live. People may argue with our words but they can't argue with our lives. Jesus said, "You are the light of the world. ... Let your light shine before men, that they may see your good deeds and praise your Father in heaven" (Matthew 5:14,16).