Mental Health Diagnosis

My mother over the last 10 years has believed she is a god. She can go from happy to extremely depressed. She has stopped contact with most friends. She refuses to work, as it goes against her belief that she is a god, and the plans that go along with that idea. She has spoken of seeing witches and demons, and has talked of feeling them touch her, or assault her.

My grandparents and uncles believe she is bipolar. I honestly have no idea, although it is apparent something is wrong. This all started occuring right as my mother was entering menopause and as my parents were getting a divorce.

I would like to know what is causing this, she was an amazing mother before hand, and the switch was rather sudden although it has gotten progressively worse. What options do I have to better diagnose the problem when she believes nothing is wrong with her? How can I improve her quality of life?