How do you convince someone with obvious mental health issues to seek treatment?

Even if you convince them, if they don't want it themselves, they will find every bad thing they can about it unfortunately... At least that's my experience as the best friend of a girl with nervous anorexia. She agreed to aknowledge the problem and go to psychologists and psychiatrists, but she never liked any of them and she always feels the need to stop seeing them because they're not being helpful.