Some people, including my wife, have a problem with carbohydrates and need to regulate their insulin production by limiting carbohydrate intake in the morning and afternoon. If she typically becomes very hungry and then very tired a couple of hours after eating carbs in the morning, she may like The Carbohydrate addicts diet. This diet limits carbohydrates until dinner time causing the dieter to feel full very quickly, have a burst of energy before bed time, and then sleep more soundly at bedtime. But take my advice and don't tell her to try it. Do it yourself and let her ask you about it.
Women hate hearing fitness or dieting advice from their husband or boyfriend.
I learned that the hard way. The only way to do it is to make permanent changes. To make permanent changes you must take very small steps. Make one small change a week maybe. Oh, and you shouldn't exercise every day.