Our children don't always make wise decisions or live the way we know they should, but they're still our children, and if possible we should do all we can to maintain a relationship with them. Jesus urged us to "be at peace with each other" (Mark 9:50).
Does this mean you ignore what your daughter is doing or keep quiet about your concerns? No, it doesn't, and the reason is because you love her, and you know from your experience (and from God's Word) that eventually her sin and rebellion will catch up with her. Right now, she thinks she's found the road to happiness, but in reality, she hasn't. Ignoring God's moral laws and choosing to live only for the pleasures of this life eventually lead to instability and heartache and unhappiness. The Bible's warning is true: "'There is no peace,' says my God, 'for the wicked'" (Isaiah 57:21).
Be thankful your daughter still wants to share in your family's life. Far too many in her situation become alienated from their families, and when troubles come, they have nowhere to turn. At the same time, don't give her the impression that you aren't concerned about the road she's traveling -- because you are.
You may feel helpless right now, but remember: God is able to do what we parents can't do. Pray for your daughter, that she'll see the error of her ways, and most of all, that she'll turn to Christ and commit her life to Him.