My friend's cat stopped eating

My friend’s cat’s birthday is April 21st, 2020. She’s drooling, not eating, growling at her food and losing weight. At first the vet said she has a respiratory infection, fever and ulcers in her mouth; then put her on antibiotics, liquid and powder with food, but she’s still the same. It’s been about 3 weeks, the vets also said her teeth were fine, she’s in emerge now, but still nothing; the vets are saying she’s fine.