I have a friend who has a huge depression problem and I don't know how to help her. What should I do?

I am going to call her Stacy. She has been depressed for a year now, and I still don't know what her problem is. She isn't sleeping well, losing interest towards everything she loved, pushing her friends away, including me, and refusing to eat. Thank god, she hasn't been thinking about suicide. I try to do my best to get her to talking to us because we are worried for her. Nothing is working. I'm not going to give up on her, but I really wish she would tell me. Is it my fault? What can I say, so I can make her tell me? Stacy keeps repeating that, "you will hate me, if you knew" and I keep telling her "I won't" I'm exhausted and I am just running out of plans.