There's a pretty big difference in calories and fat between the Fromm formulas and the Canidae Platinum. Canidae is 330 calories per cup and 8.5% fat whereas the Fromm Classic Mature Adult is 388 calories per cup and 11% fat while the Fromm Gold Reduced Activity is still 367 calories per cup and 11% fat. That means you would be giving her 37 calories per cup more on Fromm Classic Mature than on Canidae. If, for instance, she eats 5 cups per day that's like feeding her an extra 1/2 cup of food per day. In a week's time that's 3 1/2 extra cups of food.
In the example above, if you cut out 1/2 cup of food per day, cutting from 5 to 4 1/2, would she start to feel hungry? If not, great. If so, though, you could try to fill her up with some non-fat options like cooked green beans, carrots, broccoli, cauliflower.
Canidae is presently made by Diamond. However, they are working hard to get their own manufacturing facility up and running which should make their food a lot safer. But I don't know when that facility will start operating.