Thanks for your patience. I took some time and looked everything over carefully. So it is clear that Eva has suffered from GI upset since you've had her (i.e. vomiting hairballs, troubles with constipation and more recently diarrhea). In addition, she has developed kidney disease over the last 6 months based on her lab work. Please note that in April of 2016 Eva's creatinine was normal at 1.5, her SDMA was normal at 13 and her BUN (which had to be calculated from the BUN/Crea ratio) was elevated at 58.5. The mismatch of normal creatinine and elevated BUN suggests dehydration and likely GI ulceration/bleeding which raises BUN. At that time, her thyroid level was 2.3 which is in the grey zone for hyperthyroidism. For cats with ANY symptoms of hyperthyroidism, it would be appropriate to run a Free T4 by Equilibrium dialysis to rule-out thyroid disease. Symptoms include but are not limited to weight loss with good appetite, increased thirst/urination, vomiting, diarrhea, anxious/restless, etc. Not all cats exhibit all symptoms so I'll generally act on the side of caution and rule-out hyperthyroidism in any cat that has a grey zone value unless they are 100% healthy or have been definitively diagnosed with another disease that explains all their symptoms in which case I simply recheck the Total T4 in 3 months to assess for emerging hyperthyroidism. Hyperthyroidism is the most common endocrine disease among cats so it should really never go undetected. Please note that while hyperthyroidism generally decreases kidney values I have seen the values decrease after treatment for hyperthyroidism.
In July, her BUN was 48 and her creatinine was 1.8 with a low urine specific gravity of 1.018 which is the first time she is officially diagnosed with renal failure (i.e. stage 2). She had no protein in her urine at this time. In August, Eva's kidney values increased. On Aug 19th her kidney values revealed her BUN was 41 and her creatinine was 2.5 (no SDMA). Values over 2.0 are considered stage 3 renal disease. However, she was diagnosed with a urinary tract infection on August 24th which was likely present on August 19th and may have played some role in elevation of her kidney values (i.e. kidney infection present?). Her urine protein creatinine ratio (UPC) was 0.19 at this time but the significance of this cannot be determined in the presence of infection.
My recommendations for additional diagnostics would be to repeat renal values (BUN, Crea, SDMA, Phos & potassium)and repeat a urinalysis with UPC as well as a urine culture. You need to see that the enterococcus infection resolved and learn what the kidney values/urine protein levels are since that has been achieved. This is the only way to know if Benazepril is needed or not. Conversely, if the infection persists, then obviously further treatment will be necessary. The lab work should be ideally performed just before you are due to give fluids again: in that way, you see the worst case scenario without the fluids diluting the values. In addition, Eva needs a repeat Total T4 test and if the value falls in the grey zone again, then she needs a Free T4 by Equilibrium Dialysis (a plain Free T4 test is less accurate).
I did check on Renafood supplement: there are no studies regarding its use. However, various veterinary specialists state that it is very safe and I have never seen it harm any patient. Since it is a food supplement, allergies are a possiblity but not commonly encountered.
Gray stool can be the result of constipation (i.e. the gut has extra time to remove the urobilinogen from the stool which usually provides the brown color OR increased fat in the feces. It is not an emergency at all but suggests some intestinal disorder is ongoing. The increased frequency of bowel movements that you have observed recently suggests her large bowel is inflamed and of course the borborygmi (i.e. increased gut sounds) suggest inflammation further up in the stomach/small intestine. Based on Eva's history of GI issues well before any kidney disease developed, I believe this is a separate issue that needs to be addressed apart from her kidney disease. Again, hyperthyoridism if present or emerging would complicate any underlying GI issue so this must be ruled out.
For cats with chronic GI issues, the first step I take is dietary modification. I recommend chicken and turkey canned diets only: no beef and absolutely no fish. The diets should be at least 50% protein and preferably less than 10% carbohydrate. Sometimes it is necessary to find diets that eliminate guar gum and carrageenan as some cats are sensitive to these additives that are used to thicken the canned food, but I usually don't start out on that type of diet because it may not be necessary and those are harder to find, more expensive, etc. A few cats are senstive to chicken and turkey and require a more novel protein like rabbit: again, I don't start out on a rabbit diet but consider it if the initial changes don't help. Grains can also be eliminated but in general the idea is less than 10% carbohydrates. Cats are obligate carnivores and protein is what their GI tracts are made to digest. This kind of diet is directly opposed to what k/d is trying to accomplish. However, when you are dealing with cats that have multiple issues, prescription kidney diets are not always possible. Less than 10% of my feline renal failure cats eat prescription renal food. This is not because they all have other special diet needs BUT rather because cats don't like renal diets very much and older cats tend to lose muscle mass anyway. So if you feed an elderly cat with kidney disease a food low in protein, they lose weight and it is mostly muscle. Sarcopenia in geriatric cats is a big issue and hard to reverse. I like my patients with renal disease to eat well and maintain their weight: maybe even be chubby. Remember, the low protein renal diet doesn't stop or reverse renal disease, but it simply aims to decrease the BUN (by product of protein metabolism). It has less phosphorus too, but lower phosphorus and BUN can be achieved through other means. These include using subcutaneous fluids, phosphate binders and supplements like Azodyl. I don't recommend those for Eva at this time because she needs the recheck lab work to assess her post-urinary tract infection values first.
In addition, for Eva's GI issues, I'd recommend Pepcid AC (i.e. generic name famotidine) at 5mg once daily. This is a very safe antacid medication used for cats with GI issues and also commonly used for cats with renal issues. An alternative to Pepcid, in the event Eva doesn't like to take Pepcid or it is difficult to give her, is Prilosec (i.e. generic name omeprazole) at 5mg every 12 hours. Sucralfate tablets at 1/8 tablet every 12 hours can be very helpful in resolving diarrhea in cat: it is not absorbed by the body but simply coats the intestinal mucosa and binds toxins as well. It is important to monitor for constipation and decrease the Sucralfate dose if needed. Sucralfate should be given 1-2 hours before or after other medications to prevent decreased absorption of of other drugs. I'd also advise a probiotic. Fortiflora is a great choice (i.e. is said to be hypoallergenic) but it has to be mixed with food and some cats don't like that. You may be able to increase its acceptance by dissolving it in 1/4 teaspoon of water and make a gravy to mix with food. I have trended toward Vetri Science GI Balance Pro since most cats take it as a treat: http://vetriproline.com/gi-balance-pro/ The Mega Probiotic that you sent an image of is fine to but then the gritty texture could be an issue as with Fortiflora. All these probiotics are available on Amazon.com and as a bonus they are one means of preventing urinary tract infection.