I am so mad for you. Personally, and others may disagree, I think it's BULL that they kept your cat overnight for a pee sample. Pure bull. Any vet or tech worth their salt should be able to obtain urine via cystocentesis (with a needle). If she didn't have a big enough bladder they could have sent you home with No-Sorb litter and told you to keep her in the bathroom with a litterbox overnight so you could collect the urine. In all my years....oh, I'm so mad for you.
The rabies vaccine thing was bunk, too. Most states allow 3 years for rabies vaccines, unless it's Purevax, at which point it's one year. No vet with half a brain denies an animal care due to vaccine status. We HAVE TO see unvaccinated sick animals all the time. You shoud NOT give a vaccine to a sick animal. It's bad for their immune system. Rabies is the only vaccine required by law. You don't need to get the FVRCP shot if you choose. I'm surprised they wouldn't let you do a home quarantine, but I know that varies by state.
Have you looked into Care Credit? A lot of vets I know will end up working a billing plan.
One thing I will say about the biting - I have 4 very sweet cats. They deal with my 3 year old on a daily basis and have never moved to swat, scratch, bite or even hiss at him. They are very gentle and easy going cats. This all changes at the clinic. My sweetest, most carefree and loving dopey cat, Gawain, will absolutely try to eat anyone who comes near him. The clinic is a scary place. It's loud, it smells and there are these people who shove things in your butt and horrible meds down your throat. Even the nicest pets can turn aggressive while at the vet. Many owners are embarrassed when their pets act like that at the clinic, but I tell them not to worry as all of my cats have lased out like that.
All in all, I'm so sorry you are going through this. When she is home, make sure she has plenty of fresh water at all times and that she is drinking. I personally think there is a lot of overkill with prescription urinary diets. Plus, those foods (Science Diet, Royal Canin, Iams) have crappy ingredients and chemicals in their food. Science Diet loads their urinary diet up with sodium in order to get the cats to drink more. And the majority of them have chemicals. My two males have FUS and required surgery to remove their penises. I don't have them on a special diet (I feed Blue Buffalo Spa Select Holistic) and they have done well on it for years. I second the craberry treats. I hope everything works out with your dear kitty. And when this is all said and done, please find a new vet if possible.
