Has she had a senior workup? Lab work? Dental check? X-rays if indicated?
There are many reasons why this would happen. Only a veterinarian that examines your dog can diagnose.
I would make an appointment with a veterinarian close to home, asap, that would be a good place to start.
Find a veterinarian that you trust and can work with.
Sudden changes in appetite and behavior are red flags, could be something benign, or something quite serious. No one over the internet can or should try to diagnose your dog.
Best of luck.