You can take legal action against her, talk to a lawyer! My uncle was diagnosed manic depressive and went after my brother-in-law such that my niece and her family (her husband was a lawyer) had to take action against him. As you say, it is not your fault and does not make sense; she is sick!

I am glad you have a good support network; learn of your father and how he is doing through your brother or someone else "safe" but keep her from calling your office, legally. I am sure your company does not want you working upset and perhaps can help screen once you have a restraining order against her. The managing Vice President of the company I worked for had a problem with an ex-girlfriend and finally told us (we answered the phone and knew to screen her out but she'd disguise her voice/the way she asked for him and occasionally get through) his difficulties and we felt "closer" to him and much more inclined to help/ask "who's calling" and check out female callers better, etc.