Has Fluffy suddenly turned into an "I won't eat anything" cat? A finicky cat is not the same thing as a cat who won't eat at all. Let your cat "diet" for a day if he feels like it, but anything longer than that requires an intervention.
Put kitty in her carrier and drive to the vet. Cats won't go into self-imposed diets. If yours decided to stop eating, something's wrong. Loss of appetite can be due to many things, from cardiac failure to poisoning to icky worms. If the appetite loss is due to a medical issue, addressing that issue will help solve the problem.
Make the food as "stinky" as possible. Cats won't eat if the food doesn't smell good to them first. A few seconds in the microwave for wet food should do the trick. Or add some canned tuna or a bit of baby food to the mix. If all fails, try a different brand or a different flavor of food.
Sprinkle some catnip on the food. Aside from getting your cat all hyper and happy, catnip can also stimulate appetite. If your cat is not convinced that eating catnip is the way to go, just get her a toy full of catnip and let her play with it for a few minutes, right before offering her food.
Serve your cat some scrambled egg whites. Egg whites are an excellent source of complete protein, which cats need to stay healthy. Even picky eaters tend to like eggs, so it might inspire your kitty to eat, even if she's not hungry at first.