It has a lot less to do with the amount of food, than the amount of exercise. I'll bet she isn't nearly as active as she used to be.
The worst part of inactivity is that it kills muscle mass, so what ever is eaten gets stored as fat.
Then people diet, and don't increase their exercise, and lose even more muscle mass, then they get even more fat when they go off the diet that isn't working for them because they aren't exercising.
Or worse yet, they join some kind of aerobics class, which is worse than worthless, because it just overtrains, and cause even more muscle loss...
Sorry, I'm ceritified in exercise nutrition, and I see it all the time. Its pretty frustrating to listen to people (women) whine about getting fat, but if you suggest that they pick up a weight, then they freak out because they "don't want to look like one of those bodybuilders". Like that's ever going to happen...
Get her out of the house and back in the pool.