I do not want to alarm you, and I am not a vet , but you must get your cat to a vet as soon as possible.I have had a lot of experience with my own cats over the years, and renal failure is very,very common in elderly cats. the symptoms you describe are exactly what I have witnessed with several of my own cats. Unfortunately with kidney disease, the symptoms dont usually show until the very late stages. I hope and pray that I am wrong, and am even debating as I typing this if I should even be telling you this. But you have asked the question, but if you love your pet you will want to get her some help asap. I know it is hard and frightening, but you do not want her to suffer any more or longer than necessary. She is obviously ill, and if I was in your position, I would take her to an emergency vet. If you phone your own vet now, if there is no one there they will probably have an emergency number on a recorded message that you can call. At least give them a call, and they would be able to advise you better than I can.
I hope it is not as serious as it sounds. Please let us know, what you decide to do, and the outcome. Meanwhile, I will be thinking about you, and I really hope that your pussy cat gets well again. Good Luck