I've known 2 people who have been on Atkins diet, their breath stank due to ketones, 'pear drops' or 'sweet' is a very polite way of putting it. Putrid is far more accurate imo. From a quick look on Wikipedia, it seems ketones can also be in sweat so that could also smell I guess.
Does your wife check for ketones when you can smell this smell?
Could it be the insulin leaking from the pump somehow? Insulin smells very odd, I don't know how the pumps work but I assume your wife has insulin pens as back-up, get her to squirt some out (sorry I know that sounds wrong but I can't think of a less dodgy way of putting it!) and compare the smell.
Has your wife changed her diet at all? Lots of things you eat can effect your body odour.
You say it is like she is passing wind repeatedly, does it smell like flatulence? It might be, lots of things can cause increased flatulence.
Has your wife been to a GP about this?
Finally, are you 100% sure you only smell the smell when your wife is there? Has anyone else said they can smell it? If no-one else can, you should probably mention this to your GP, just in case.