Not everyone has the same caloric requirements. To lose weight, we obviously need an
energy debt.
That said, suppose your wife needs 1500
calories to lose weight and you need 2500.
Also assume you are both eating roughly 2000 cals.
Net result.
You lose.
She gains.
Very simplistic numbers, but just to prove my point. To give more specific recommendations, I suggest providing us with both of your stats as well as a general idea of how many
calories you are eating.
Have you seen sites such as
FitDay - Free Weight Loss and Diet Journal or
CalorieKing - Diet and weight loss. Calorie Counter and more. 
