The most important thing you can do for your friend is to pray for her, asking God to open her eyes to the truth and point her to Christ, who alone can satisfy her spiritual hunger. God can do what we can't do, even breaking through the deep resistance some people have toward Christ.
In my experience, people who become involved in cults or other forms of non-Christian spirituality are often very resistant to the Gospel -- at least at first. Down inside, they often have a deep spiritual hunger, and for a time they may believe they've found the answer to it. They also don't want to admit they might be wrong, and their pride gets in the way. This is why simply arguing with them seldom accomplishes anything. Instead, the Bible says, "A gentle tongue can break a bone" (Proverbs 25:15).
Let your friend know that you care for her and still want to be her friend, in spite of her hostility. At the same time, don't open yourself to her lifestyle or be misled by her arguments.
Instead, ask God to help you be an example to her of Christ's love and peace. The Bible says, "In everything set them an example by doing what is good" (Titus 2:7). In time she may realize she's on the wrong road, and she'll be more open to your witness.