I am a middle-aged married woman. I believe that you truly need to accept your wife as she is. You say that you are repulsed by her obesity. I am sure she has picked up on this. I've found that when people stop doing the things that they once enjoyed it's either because they're depressed or because something caused them to be insecure about doing these things. Low self-esteem can be a vicious cycle, leading to unhealthy and self-destructive behaviors. You also say that "she resents your controlling ways". Can you try to stop controlling? Can you tell her that she is the love of your life and you only want her to be healthy and happy?
I am also a big fan of therapy, as a receiver myself.
Good luck.