Involuntary Hospitalisation - how to help family member

My sister has been involuntary hospitalized after experiencing delusions. She was diagnosed with Borderline Personality Disorder a while back. She has never accepted the diagnosis or accepted treatment.

Recently she started experiencing delusions that people were trying to harm her. It resulted in the Hospitalisation after the people she was accusing called the police and NSW health over a concern for her mental health

How can we support her? Currently she’s refusing communication with the family? How can we work with the hospital system to best establish a plan.