Saving a friend

One of my very good friends that I have became very close with in a very short time has started to go down a bad path and has let the people around her influence her. I am trying to be there for her as much as possible especially now more then ever since the only good friends she had seemed to be fake and don't talk to her any more, so in this time of need I'm the only one there for her and I have no problem being that person but she is bringing me down with her which isn't a good choice for me, but I feel like I can't do anything that is going to make a huge change. I have done all I feel I can and it doesn't seem to effect her even though she says she will change, me nor others seem to see it in her. I want to try to help her and put her back on the right path which she once knew because she has a lot of potential, but I must be the only one who sees it in her, she must not. She has been lying to cover up her mistakes but those lies are leading to more lies which are getting her deeper and deeper into this bad situation. In heart she is a really good person but has just made some bad decisions in the past. She used to go to a private school which she has now returned to due to her mothers choice which was chosen because of Edina's bad reflection on her, when she feel in to the wrong crowd. I feel like she is trying to change but it's not doing any good because she is worrying about everyone but herself but then again she is worrying about no one but herself as well. It was such a drastic change if you would have known her 45 months ago you wouldn't believe it's the same person, it's crazy how much the people around you can change you sometimes for the better but in this case for the wrong. She is tearing the real people who care about her the most away from her which is sad to see. I'm stuck in the middle of the whole situation I can't dismiss her because I'm one of the only people she has and she needs me now more then ever, but I also can't get caught up in she drama either because as much talking to her I can do to help change her not much of it will actually influence her and her decisions that she will make.