Type 1 or Type 2 diabetic?
I'm a Type 1, and have been to Food and Wine for the past few years, and thoroughly enjoyed myself. F&W is actually a pretty good time because the portion sizes at the booths are small, so I am, at worst, getting a few grams of carbs in a dish (probably less than 15g most places) as opposed to getting 75g or so in a full meal. Plus, they're spread out over a longer time period, so it's not all hitting my system at once.
Another thing: You are going to be doing a lot more walking than you probably usually do, so you are getting more exercise and burning more calories, which means that your wife will need to adjust medication, if she is taking any.
My general rule is that fewer carbs are better, but 0 carbs is not as much fun, so I plan when I'm going to get those carbs. So, instead of getting the lobster roll with all that roll, I'd get the lobster claw cuddler. Then I'd get baklava later. Not an even trade, but I'd be better off than I would be if I'd gotten both carb-laden things.
Also, just in general, beware of the diabetic or sugar-free options for desserts. These can still have a lot of carbs. Sometimes even more than an equivalent sugar-full option. I just ran into this looking at salt-water taffy recently, though not at WDW.
Diabetes doesn't destroy your ability to enjoy WDW, and doesn't even destroy your ability to enjoy food at WDW. You may need to prioritize more than if you didn't have to worry as much about the content of the food, but your planning will pay off in better health and fewer feelings of guilt. At least, that's how it works for me.
I'm happy to answer any questions you or your wife have.