What else can I [37 M] do to encourage my [35 F] wife on her weight loss/personal growth journey?

Throwaway because my wife knows my main account.

Background My wife and I have now been together for nearly 9 years, married for 8 and with a 3.5 year old child. Outside of some causal encounters, this was my first relationship after separating from my high school sweetheart (we were together for 8 years, and she, rightfully so, instigated the separation/divorce). There was a gap of about 18 months between when I separated and when I started dating my now-wife. After the separation I started making some solid life changes: I quit smoking (my ex was a smoker too but had refused to quit) and started working out (my ex was also not big into being active, nor was I at the time). It's worth mentioning that my ex and I were very codependent on each other, often with detrimental consequences, and now that I was "free" I wanted to start embracing positive change.

Dating Being honest, I almost bailed before the first date with my now-wife began. I saw her first and was disappointed that her online profile pictures weren't really representative of her. While I like thick women, she was/is obese and was physically bigger than her profile pictures led on. However, she had a great personality and I wanted to see where things would lead. As we got to know each other, I came to learn that she had always been overweight but wanted desperately to get in shape. I thought this was perfect - we could go on this incredible journey together. Unfortunately, I made a few mistakes and very quickly fell back into being codependent - we moved in after less than a month of dating, got engaged within 6 months, and married 2 months after that. I feel that the "trajectory", for lack of a better word, I was on before meeting my wife ended up constricting and if I had to do things again I'd do them differently.

Today At 37, I am now probably in the best shape of my life. My wife, meanwhile, is still obese. She's tried so many different things (e.g. Atkins, The Zone, South Beach, MyFitnessPal, going vegan, Susan Powter, talking to a bariatric specialist, etc.), both since we've been together and prior to dating. Things are great when they work, but as soon as things start getting tough, she shits all over whatever she was doing and then quits for months at a time. For example, even though she felt better on a vegan diet, she quit because her body craved meat. Also, despite having a medical professional encourage her to lift weights, when she tweaked her knee she gave all exercise up for 7 months. There's always something, and by now I have very little tolerance for what I see as her excuses. I know she struggles, and for the first few years I tried my best to support her, but now I'm just resentful and don't care. I've told her as much - that she lacks tenacity; that whenever things get a little bit tough, she quits. I now feel like a dupe, strung along by someone who talks a mean game. I'm incredibly angry that some of the things I was promised may never come true. For example, the active lifestyle I sought, that I wanted in a partner, and that I was promised, is now all but a pipe dream.

Complicating things is that my wife's laissez faire attitude isn't just related to her weight. It carries over into other areas of her life. As another example, she started taking a distance ed. course but very quickly stopped putting any effort into it and had to drop it. Overall, the best way to describe things is that, if they don't come easy, my wife quickly loses interest or doesn't bother.

Moving Forward There's a lot of reasons why I want to fix things: I'm still emotionally attracted to my wife; we get along great; our day-to-day routine works well; and we have a child together. But, as time goes, on I yearn for the physical attraction and the push to be the best I can be. That all said, if we didn't have a kid I think things would be different and I don't know if we'd still be together. She's tried/is in therapy and has a prescription for anti-depressants but doesn't want to take them because they'll mess with her chemistry. Meanwhile, here I am, wondering what else I can do? Also, every time I try to offer my wife an out (i.e., "maybe we'll just live two different lifestyles") she gets very defensive and always reaffirms her commitment to trying.

Edit: To clarify, attempts at talking to my wife about what I can do to help her end up no where.

tl;dr: My wife gets easily discouraged, affecting her weight loss and personal development. Years of me trying to support her have left me angry and resentful. What can I do?