Hey there, I found this post while searching the internet for the EXACT same problem. My wife has been depressed on and off for the decade we've been together, however, since the birth of our daughter (her second child, my first) 6 years ago, she has been suffering from depression. I really believe it is post partum (sp?) but I am no doctor.
I have, however, spent a lot of time in therapy because of my co-dependency issues, etc, and have gotten a lot of help.
Like the OP, my wife is exactly the same way... she has put on around 70 - 80 lbs and she believes this to be the cause of her depression. I believe it is a symptom OF her depression. She refuses to get help, she gets angry when I approach her with my concerns and seems to not care if I am here or not.
This is breaking my heart, I love her with all my heart and don't want to leave, but I am at my wits end and ready to walk out the door. She DID buy a couple books on depression, so in some way, I consider that a small victory, as she is at least acknowledging she has an issue.
However, she doesn't read often and based on what I have seen, has ZERO self discipline to do things on her own when it comes to bettering herself, because first she must admit she was wrong, which she WILL NOT DO. I keep praying she will see how much she means to me. I pray that I won't have to be alone in my own house and I pray that when I bring this up, she doesn't look at me like she could spit in my face. I love my family but I hate being alone, even in a room with her in it.