I am shocked by this trhead!
I used to 'hate' my mother, but not because she was dead weight as you said, but because she was physically, mentally and emotionally abusive since I was in single digits. I carry that feeling for years and it felt I was carrying something on my back and didn't leave me. I was fortunate enough to have the senses and think that if my mother died, I would have had that feeling for the rest of my life and I certainly didn't want that. I have forgiving my mother and not only that, I found LOVE for my mother and I have to tell you, I never felt better. I am free and happy.
I suggest to your wife, that whatever it is that's making her hate her mother, and I guaranty you is not the food she's consuming or the space she's taking; is something she's holding from her childhood. I suggest she resolves that and cleans it out, because when her mother dies, she'll have lots of regrets and there's nothing she could do at that point.
No, I could never live with my mother, but I forgave her and better yet, I don't have to live wit those negative feelings that were consuming me. It's obviously consuming you or you wouldn't have to start a thread on it.