I'm thankful for your concern for your friend, and especially for your desire to pray for her. I hope you won't think of prayer as a last resort, however; it should be the first thing we do when we face difficult circumstances.
When I read your letter, my first reaction was to thank God for working in your heart and life. No, you aren't religious right now but I believe God has put within you this desire to turn to Him and pray for your friend. Why has He done this? The reason is because God loves you just as He loves your friend and He yearns for you to discover His love and give your life to Christ. I suspect your friend is praying you will do this.
How do I know God loves you? I know it because He sent His only Son into the world to die for your sins. Only one thing separates us from God, and that is our sin. But Christ came to take away our sins, and He did this by taking upon Himself the penalty we deserve. The Bible says, "For Christ died for sins once for all, the righteous for the unrighteous, to bring you to God" (1 Peter 3:18).
Yes, pray for your friend but most of all, pray for yourself. Don't turn your back on God, but by a simple prayer of faith ask Christ to come into your life today. Then tell your friend what you have done, for nothing could encourage her more.