There may be nothing you can do. Very difficult, but unless she's a such a grave danger to herself or others that the courts have to step in to impose a conservatorship or guardianship over her, she is an independent adult, and legally capable of making her own decisions, even if that decision is not what you would want to see her make.
Beating your head against the way trying to nag, plead, beg, cajole, etc. is just an exercise in futility. It will get you nowhere but angry, and that's no way to live your own life. Do yourself a favor and disengage from trying to "save" her. It will never succeed.