The best way to help a depressed friend is being Understanding, Patient and Compassionate.
Don’t buy the myth that somebody who talks about suicide will never do it. Take it seriously. More than 70% of all completed suicides talked or did things to indicate to others that they were in deep pain. That’s what suicide feeling is all about: a huge and almost uncontrolled pain, versus a lack of pain-coping resources. The only way to help your friend, is to help her to eliminate the pain (real or imaginary), or feed her with more pain-coping resources.
Suicidal behavior is a red sign. Somebody is crying for help. When your friend talks about her feelings, I am sure she does in an ambivalent way; one side wants to live, another die. The side which wants die is more likely the one that want a relief from the pain she is experiencing.
Don’t try to solve the problem on your own.
Seek for professional help and don’t let the person alone. Also, make sure her house is detoxified, getting rid of the means of committing suicide, if there is any at home.
Listen. Avoid arguments and advices. Don’t judge. Don’t say anything that may the person feel guilty or inappropriate. Be there for your friend and show how much you care. Embrace her emotionally, spiritually and physically; it can be extremely helpful. As I have already mentioned, look for protection and professional support for you and for the person you are trying to help.
Pray for this person. Pray with her. God’s love is the best healing for all maladies.