I'm Concerned Friend...I don't know how to help my best friend?

Call the police. They will take her, and see to it that she receives the help she needs. She is a danger to herself, that is obvious. She isn't willing to change on her own, won't listen to friends. She needs more than an intervention, she needs psychiatric help, and sadly it needs to be done against her will. Later on she will thank you for it, but it may not be for years, or over decade.