I've tried this, and it sucked about 3 years of my personal life away forever. Turns out I was the one who needed therapy after all was said and done, because I put myself out there, and tried to help her with a similar problem. It didnt help that it was mostly long distance, and that I was a gullible, sensitive little boy at the time. (it happened when I was 16, i'm now 23) All I can suggest really, is what Janos said. It's a two-way street, and if she's dodging or avoiding you for some reason, and cannot face the problem at hand and discuss it, YOU shouldnt waste your time on her. It's not worth the stress, mulling it over and over in your head, wanting to help someone in need that does not reciprocate.
Feel free to ignore my post, but I just wanted to say, I kinda know how you feel, at least have an idea, and just what might happen at the end of it all. You might try so hard to make things work, and even in the end, it still wont work out the way you'd like it to. If it's not working out now, you might be better off letting it go right now, rather than later.