A 10kg cat is a 22# pound cat, which is certainly not underweight, but is obese, so I am assuming this is a typo. If your
cat is
not eating or drinking, then this is an emergency, and your cat should go to the veterinarian ASAP. The excessive licking may be due to fleas, allergies, or anxiety (or a combination), and your veterinarian can examine her to tell you the best course of treatment.