@Danny67,
Maybe your wife feels you do contribute to sabotaging her diet or her attempts to keep her weight down. Partners can do that sought of thing, sometimes without even being aware of it.
Instead of wondering whether she is wrong to blame you, just respond to what she is feeling--she's feeling depressed because she's putting on weight. Ask her how you can help her lose weight. If it involves not having certain types of food in the house, would you be willing to give those up for a while, and substitute healthier or lower calorie alternatives?
How do you feel about her weight gain? Do you find her less attractive, or can you honestly reassure her you love her just as much, and she looks just as good to you, if she gains a few pounds?
Focus on how you can help her, and tell her you want to help her, that will both stop the blame game, and the resentment it can create.