IF she is not mentally competent, which is much more than merely that she has psychological or emotional issues or is engaged in self-destructive behavior. She must be so mentally or cognitively impaired in some way as to be unable to understand her actions or their consequences. If there is medical evicence (e.g. from treating physicians) that she is at that level of impaired understanding, it may be possible to have a court declare her legally incompetent and appoint someone as her guardian. To explore or understand this option better, consult with an attorney who handles cases involving the disabled.