The best thing you can do for your friend is spend time with her. I've noticed that people who are having trouble leading a good life get the biggest benefit from spending time with someone who is a good influence. Its hard to smoke when the person that is with you doesn't. Its hard to drink or have sex if there's no one to drink or have sex with. And if your friend is constantly hearing about how enjoyable it is to lead a Godly life, then it will only pique her interest to discover more. And, as always, I must stress that praying for her does a LOT of good. Also...
I think a helpful angel is on their way to help you with your situation. A woman in her early forties who often dresses in a big overcoat with a big belt around it will help provide the mentor role model that this young woman needs. And of course, I will be praying for her as well.
Love and Prayers, Shay