((BJ))
I'm so sorry your friend could find no alternative to relieving her pain. If you had dropped everything and rushed to her side, it might have delayed her actions - but only for that one night. You might have been able to relieve her pain for that one night, but you would not have been able to give her a will to live. You were her friend, not her savior.
All in all, you served your friend well. You provided her with a little sunshine, and she knew you cared about her. Sometimes that's all a friend can do - sometimes it's enough, sometimes it's not.