I would just cut back on the amounts your feeding, and look for the kcals per cup on the back of the bag, and match it to feeding for her ideal weight. For example, lets say she weighs 50lbs, and you want her to weigh 40. Figure out how many kcals a 40lb dog needs per day, and then match that to how many kcal per cup of the food (I think DFA has a calculator floating around here for that) to see what you should be feeding, as each variety of food varies in its kcal amount. Also factor in any treats she may be getting and any table scraps, as they count towards her total caloric intake.
Some dogs need to be fed less than the amounts suggested just because they are so prone to weight gain unfortunately. Just as some dogs need to be fed more if they have difficulty keeping weight on.
