I am sorry to hear you are worried about Big Time. I am a veterinarian and will do my best to help.
Is she at least drinking water, so she is not getting dehydrated?
There are some good appetite stimulants for cats, prescription medication like cyproheptadine, mirtazapine, and diazepam.
Usually when a cat won't eat, they are telling us that they are sick. Often the only symptom in older cats of cancer, heart disease, kidney disease, infections, etc. is loss of appetite. Cats try to be secretive about not feeling good, and then when they finally feel so bad they can't hide it any longer, they "suddenly" stop eating. If this were my own cat, I would be doing some basic blood tests to find the underlying condition, and treat it. Often that is the only way to get her eating again.
You can check to see if she is dehydrated by gently pinching skin over her shoulders and letting go. The skin should go back in less than one second; if it takes longer she is dehydrated and that would suppress her appetite.
Check her gums; they should be bright pink. If her gums look pale, that is a sign of internal illness.
Let me know what else I can help with or answer, and how she is doing.