Hi, I am Dr. Peter and would like to help.
1- Does she have diarrhea?
2- Did they do any xrays or abdominal ultrasound?
3- I assume all the blood work was normal?
An over active thyroid (hyperthyroidism) is one of the most common causes for increase appetite and weight loss. Other conditions with similar symptoms would be malabsorption/malassimilation, exocrine pancreatic insufficiency, bacterial over growth, inflammatory bowel disease, and even cancer. I would recommend you speak to your family veterinarian about performing an abdominal ultrasound to look a little closer at the abdomen and make certain everything is within normal limits. If the ultrasound is normal, than your vet will proceed to work up for the other above mentioned conditions. In the meantime, I would recommend consider switching her to a grain free diet either commercial or feed at home boiled boneless chicken (75%) with some potato or rice.
If you have additional questions I will be glad to answer them.
It depends on the underlying cause of the kidney condition; this is where an ultrasound is essential for those answers. But, in general diet (k/d), fluid therapy and sometimes medications will delay the progression of the disease and the cat can live for years. It is treatable but not curable.
Your veterinarian can teach you how to give fluids under the skin as a form diuresis. As far medications there ace inhibitors to control hypertension and improve kidney perfusion. In addition, supplements (fish oil), etc.
Baytril is an antibiotic, I suspect your vet has her on it because of the WBC being elevated. I am not familiar with the Acarex.
I would recommend to wait on the fish oil. Though it is a supplement it is best for your veterinarian to recommend the supplement they want to use based on her laboratory findings.