How do I handle my mother who has always been demanding ?

How do I handle my mother who has always been demanding? My mother is 78 years old, married to a man who is wheel chair bound who is 69 years old. Whenever I go to visit her she complains about her husband (not my father). She has been doing things like getting so mad that she goes for long drives, crying and acting out. I'm afraid she will some day hurt herself. What can I do to help her? For her birthday last year I asked friends and family to send her a "card shower" and she got very angry that I did that. She didn't speak to me for about 8 months. Just recently a church called me and wanted to recognize my step dad with an award and she said, and he agreed and he said, "SHUT THAT DOWN!" I didn't shut it down because the church had already gone through so much to get the award. Now I'm waiting for the next "backlash" of hatred towards me by them. What am I doing wrong with my mother and stepdad? Thanks.