I'm sorry to hear this.There are tons of cats on TCS with kidney issues; it seems to be fairly common these days. Hopefully someone with specific experience can offer you some advice.
You don't say whether the vet is suggesting an acute problem (lily toxicity, etc.) or something milder and more chronic. So, I'll assume the latter. Your vet will have the best advice for you, so ask lots of questions. The management/treatment plan he/she develops will really depend on your kitty's kidney values (BUN, creatinine, and phosphorus) on the blood work that the vet used to diagnose the problem. Some recommendations he/she might make include a diet change to a lower-protein food (high protein diets can make the kidneys worse), fluids under the skin on a regular basis (since she will be losing lots of water in her urine), pepcid (since increased urea in the blood can upset the stomach), and/or dietary binders of phosphates (if the phosphorus is high). But, the plan needs to be tailored to your kitty. Regardless of the medical treatment, I highly recommend that you have multiple litter boxes for her, as she will be urinating more than in the past, since her kidneys can't concentrate the urine the way they used to. I just lost a cat that was over 23 yrs old and was diagnosed with renal insufficiency at age 16. I hope you have similar results.
Yes, I hope it is now caused by some form of poisoning. I hope your vet will work with you and your cat. Chronic kidney failure can be treated and controlled and often the cat can still have good quality of life for a long time. I am hoping that for you and your cat. There are many folks on this site that have dealt with chronic kidney failure and I am sure you can get some good advice and help here. I am sorry you are going through this, but you have come to the right place for advice and support.
AddieBee, visit http://www.felinecrf.org/. There is SO much information on there about chronic kidney disease (CKD, or CRF) and you'll find comforting words as well. Tanya has a great site!
I'm not hugely familiar with the subject. But from what I've seen in researching other nutrition issues, the CURRENT thinking on CRF is not a low protein diet, but a highly digestible high protein diet.
Please do visit the sticky thread Laurie mentioned. I began it years ago when dealing with a kitty of mine with crf (I've had several over the years). Anne is about to update one section which links to now gone sites on values for dry and wet foods, to new/up to date set of tables I found. Tanya's feline crf site is my favorite overall (where these food tables are located).
I remain a fan of Calcitriol and currently have my Lyra on it (she has early crf). She's having *very* good results on it.
, but it does not mean an instant death sentence, My Sven lived for 3 years with CRF, and he was diagnosed when he was 13 years old.
Definitely check out the websites referenced above, as they have tons of information in them. And there are so many people on this site who have been thru (or are currently going thru) the same situation, so you are definitely not alone. Probably any questions you have, including how to interpret lab results, can be answered here. We'll help you with tips on how to get her to eat when she doesn't feel like it, how to give her Sub-q fluids at home when the necessity arises, etc, etc, etc.
I hate to say "welcome to the club", but these days, it's so common it's pathetic.