Only God knows your friend's heart, and whether or not she has sincerely given her life to Jesus Christ. We're to be wise and discerning -- but we also mustn't be harsh or judgmental. Jesus warned, "Do not judge, or you too will be judged" (Matthew 7:1).
If your friend has given her life to Jesus, then she needs your love, prayers and encouragement. God doesn't want her to depend on drugs to give her peace or escape from her problems, nor does He want her to become enslaved by them. Instead, God wants her to find her peace in Christ, and confront her problems with His help. Ask God to help you to confront her -- lovingly but clearly -- about her need to follow Him in every area of her life. The Bible urges us "to live a life worthy of the calling you have received" (Ephesians 4:1).
But if she is not a believer... if she is even deceiving herself about her commitment -- then ask God to help you point her to Jesus. Explain to her who Jesus is and what He has done for her. Explain too what we must do: repent of our sins, trust Christ as our Savior, and yield our lives to Him as Lord.
God has given this friend to you, and He has His reasons for placing you close to her. Ask Him to make you a tool in His hands, to bring the light and the transforming power of the Gospel into her life.