If 6lbs is her ideal weight, I would start with 2 cans Fancy Feast per day--either in the AM/PM as Larry suggested or a half a can 4x a day, if you can manage it (diabetics do best with frequent meals. If she starts to gain weight over her ideal weight, slowly reduce the the amount of food you're feeding until you hit the right amount. Metabolisms and activity levels can make a big difference even with cats that are the same weight, so there is a bit of trial and error involved.