Feeling so helpless!

Have you ever felt as though you were helpless when it has come to a friend who really needs you? Ever felt as though no matter what you did; it was not enough? That is how I feel right now. My friend is going through a really tough time, and I don't know how to help her, and I feel so helpless. I try to be there for her, but she won't talk to me, and I just feel like everything I do to help her makes her feel worse. I just feel so helpless and I feel like I am not a very good friend.