How can I help my poor mother?

I actually have a mom very similar to this. The most you can do is just show her how much you love and her and try to change the subject when she brings up the sad things. Also, try to get her to go to a psychologist, they really REALLY can help if she has an open mind. Mine has helped me a LOT. Maybe you can also check if she's clinically depressed, because there are pills to help for that as well. Just show her love and keep in close touch with her. :) I wish you the best of luck.