14 yr old female cat not eating well. Seems hungry and shows interest in food, but extremely picky, only nibbles at best. Has been to vet's 3 times in past two weeks -- complete bloodworkup was negative, complete xrays show possible fluid in left chest cavity, ultrasound results pending. Doctor says probable heart condition or tumor, neither of which can be treated. Other than the problem with her hardly eating at all, she is absolutely normal otherwise -- content, purring, affectionate, bathing, urinating, defecating. How can I get her to eat? She has had a B12 injection, too.