How can I help the depressed 93 year old women and her husband I am caring for?

I am the caregiver for a couple she is 93, he is 95. She has become more agitated and argumentative since the holidays. Her arguments with him are most often unreasonable and seem to be based on her wanting him to need her. She has taken a lot of frustration out on me as well. These people are my neighbosr, I have known them for years and love them like my own parents. I try to mediate the arguments and ask her how we can change things so that she will be happier. She says that she will never be happy again. When I cook or clean or do laundry she lashes out at me. She wants to do things she's done for the 69 years they've been married but can no longer do. She is legally blind and uses a walker. How do I avoid the daily confrontation? She has other caregivers as well, but I seem to be the one who gets the brunt of her anger. How do I defuse her anger and stop the endless arguing between her and her husband? I worry that the stress is bad for their health, and it certainly is difficult for me to watch.