Yoga for Obese People?

I have a relative who weighs about 400+lbs. She's in pain 24/7, depressed and constantly dwells on death. Because of her pain she can't do anything but sit or lie down ... she's been diagnosed with a degenerative bone disease. It's hard to live with her because she's stressed-out, argumentative and she's always picking fights. But she's 70 years old, so I can't walk away. I know she still has a lot of life left in her; I see it at times. When she was hospitalized a couple of years ago she lost over 100 lbs; THEN she was a different person. She wasn't in as much pain and she was happier. Now she can't exercise because she can barely move; and because she's frustrated she won't try. (Stubborn)!! Does anyone know of any yoga moves that I can teach her that'll help her mental pain, as well as her physical pain? If she feels that she can do it she'll try. I have her doing breathing exercises now, but it's not enough; I CAN'T get her away from her stress.