Your cat may be on the wrong diet, be very obese, may have food allergies, or an endocrine disorder, kidney disease or more. When a cat stops grooming it can be almost anything even heart disease, since it is a very subtle sign of something that is not quite right.
What kind of diet is your cat on?
Before going to the vet you can try the following:
Please place her on an all canned diet such as Evo/Innovo, Wellness grain free, Natures Wellness-Instinct, and others. The food you choose MUST be canned. Do not feed her ANY DRY!! It must also be very low to no carbs and grain and gluten free! You should feed her 3 meals per day, or if you can't you can leave canned food out for several hours.
Force fluids by getting a kitty water fountain, providing bowls of dilute clam juice, tuna juice and other broths.
Thank you for your response. She currently eats dry food. I give her Purina One for indoor cats formula. I will try to canned food and see how she does.