Have you taken her to a vet? I hate to say this, but it just may be getting close to her time. 19 is incredible, and you must have done a great job to give her such a long life.
An older cat does slow down on eating, but what you describe could be symptoms of cancer or just old age. Do take her to a vet if you can afford too. You don't want her to be in pain, and it is possible it's treatable.
I had a 20 year old cat that just passed away in July. He had CRF (Chronic Renal Failure). He had those same symptoms and I took him to the vet. He was just 17 or 18 at the time. With the proper food and and fluids she can live for quite awhile if this is what she has. We had to give Morris an IV bag and medicine when it first happened but then he got better and lived medicine free for about a year and a half. After that we did give him an IV bag once every three days. They adjust very fast and it's not as hard as it sounds. The fluids make them comfortable. Good luck! Keep us posted.
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