How can I help my friend with Narcissistic Personality Disorder?

Through lots of research and study, I am 100% certain that my best friend has Narcissistic Personality Disorder. We are both women in our early twenties and have been friends for 10 years. The symptoms of this disorder in her life have gotten severe enough that our friendship hardly exists anymore. She has never lived away from her parents and still lives at home, and it seems as if her maturity level lowers with the ping years. Because people with this disorder manipulate those around them to do things that are their own responsibility, I have allowed her to do this to me for years without really understanding it. It is at the point now that I don't know what to do to keep the friendship together. We hardly speak, and when we do, it is shallow and superficial, when we used to have deep conversations. If I told her that I believed she has this disorder, she would never speak to me again. I feel that she is slipping away, either to her choosing, mine, or both. She seems more depressed and upset now than ever, but since we hardly talk, it seems that any advice I offer blindsides her due to the fact that she doesn't think about the way that she behaves or acts towards others. I'm really at the end of my rope, and can hardly stand to be in the same room with her anymore. Is there anything I can do?