Fran, I wouldn't worry to much about this. Things happen in this life for a reason and God has a plan for all of us. He works in mysterious ways. I will pray for you and your daughter but I want to share that I went through a similar experience when I was growing up. I was raised a Christian, and went to Church every Sunday and some weekdays. When I went to college, a whole new world opened to me and I found myself questioning my faith and eventually I considered myself an athiest. I stopped praying. I stopped going to church. My family and friends were none to pleased with me. I graduated from college and started my career and began to live my life. Things were not going too well for me. I carried a heavy burden. One day I sat and cried from my frustrations, and I did something I hadn't done in years, I prayed. My anxiety and that burden I carried seem to be lifted off of me. No one can tell me there is no God. I know what I felt that day and how wonderful my life has been since. I believe your daughter is just exploring the world outside of what she knows. The Lord takes care of his flock and always finds the ones that stray. He will find your daughter. Just like he found me when I was lost.
Dear Heavenly Father, I pray that you guide this young woman so that she may walk in your path. Strengthen her so that she is able to keep her faith. Be in her heart so that she can not forget you. Let Jesus show her the way. In Jesus name I pray, Amen!