This happened with my ex - the kids and I, we are all built more lean and spare, but ex hung on to weight. So I cooked or he did, we all ate the same food but somehow he got fat, we stayed skinny.
Well I am like your wife, low tolerance for sweet stuff - usually when I want something sweet I want to taste it, not really eat it, if that makes sense. So yes, a big spoonful of ice cream, one twix candy & save the other one for next week. Emergency chocolate bar at work lasts a month.
Ex was the other extreme, could binge sweet foods. So even with the metabolic advantage of being a couple inches taller and male, his natural intake kept him on the heavy side.
Intermittent fasting is such a good way to maintain weight, but not if you can eat a bag of candy in your eating window!