How can I stop slander?

I have been divorced for about a year from a nurse. During our 5 year marriage, she had 2 suicide attempts and was hospitalized 2 other times for drug rehab. She was diagnosed with borderline personality disorder. She continues to work as a nurse. Recently, she has been posting derogatory things about me on a local forum. Just this past week, she has accused me of being a child molester. She does this while at work. What responsibility does the hospital have? Should I approach the hospital with this matter or should I call an attorney. I am involved in a number of civic matters and this is doing irreparable harm.