I really don't know much about liver failure, my only experience were some abnormal liver readings in ine when she was first diagnosed hyperthyroid following an out of character couple of days not eating then yellow vomiting and diarrhoea, and I rushed her to the vet fearing hepatic lipidosis. I believe the readings were hyperthyroid related from my own research though the vet thought not - ALT was expected with hyperthyroid but she also had elevated bilirubin which the vet said not but I tracked down how it could well be. And by the time further bloods were taken a fortnight later bilirubin was normal. Anyway that's by the by.
Pain from failing kidneys I believe happens at quite an advanced stage and in my limited experience seems to show by an arched back, muscle loss (that's when you feel the backbone and hip bones sticking out even if the cat's overall weight is good) and sometimes hissing when touched near the kidneys. I have always found cats in pain or under great stress (after all pain is stressful) to get dandruff near the base of the tail and the coat feels rough and possibly sheds a lot more than usual.
Pain from liver issues I'm not sure about. As I understand it some liver problems cause pain for us humans but others don't there are so many ways a liver can be underperforming, as it has so many functions. But as one of its functions is to process toxins, that's what makes me think pain meds might be not recommended if it's not working properly. Cats as you know tolerate quite a bit of pain before showing it and with this cat being new-ish to you it might be harder to spot. This is a pretty good guide to the more subtle signs of pain
https://www.preventivevet.com/cats/how- ... is-in-pain. I would say under their title 'eyes' that the face has a slightly rounded and tense look, a bit stiff. And sitting in the loaf position with all 4 feet down, combined with the facial look, would be a strong indicator of pain.
If you think she is in pain, and meds are out of the question, a heated pet mat can help some cats. Some may avoid you but some can want to be near you but not be touched, a hard thing for us to understand as we need to cuddle and comfort, but that can be too much for a cat in pain. I have heard of cats purring and even padding when they are in pain or stressed, I had never seen this is any of my cats until this hyperthyroid one who turns on the engine every tie on the way home from the vets having squeaked and mewed and yowled all the way there!
Natural remedies may have something to offer for pain but go careful if she is on other meds as seemingly innocent herbal preparations can interact badly with prescription drugs. Always check with the vet.
I never see her drink anything but she has all wet food. 