What would cause a 14 year old cat to almot screm before she drinks.?

She has lost a lot of her body mass. She is very old. i can't get her to eat any thing at all. I have other cats and i feed them in another room because the other kitten upset her. But all she does now is eat, sleep, use the litter box and sleeps more.A lot of this breed also have this type of problem . Please forgive me the gory details, but along with the sinus issues, she get mucous scabbing over her nose and I know it hurts her. Nothing cab be done. The only med that I as told to try was infants benedryl She didn't do so well with that either. But now that's she's almost 15 and can barely eat anything anyway. I get her canned pate food and make sure its where she cat eat, The last 2, should have come down to at least look at the food like she's done in the pats, I will even put her a separate dish away from the other cats so that they won;t bother her. When she has eaten, its been maybe a table spoonful two times a day, i offer her milk, goats milk, pure cow milk, I've offered her bacon ham, turkey and such. I am totally beside myself. I know in my gut that they are going to tell me to have her put down. And he would be right. She's my baby. Please, this is serious. If you would only post totally serious and helpful advice and leave the sarcasm in the car i would appreciate it. Thanks in advance for any information you can give me.