Beware, this is a long post. Here is the response from my cousin, Dr. J, the vet(hope it helps):
ooooo, I love vet questions. Bear in mind that I am NOT looking at this kitty so I cannot diagnose it. However, here are my thoughts:
12 years old is an older kitty - one of the FIRST things I would have done was check her bloodwork. She says her vet says maybe it's kidney failure. One way to get a better idea of whether it's dehydration or failure is to check urine concentration (your friend doesn't mention that they did this). IF it is strictly dehydrated, then the urine should be very concentrated because the body is trying to conserve water. IF it is FAILURE then the urine will be dilute AND the cat may also be dehydrated on top of it, but the kidneys are not conserving water as they should. While kidney values are pretty kidney "specific", they are not sensitive -- it takes about 75% of the kidneys to be hurting for these values to raise at all. It is also possible that Kitty has long standing kidney failure and has had a sudden downturn -- with only a small amount of kidney left to function, those values may only go up a little and they will be very stubborn to come down. Sometimes they don't come down to normal -- all we can hope is to make Kitty feel better.
Not sure why they won't treat her ears until she eats UNLESS she's on oral medications -- don't want to upset an already upset stomach. If she's on drops in her ears only I don't see a reason why not to treat -- but maybe they have their own reasons. Owner did not specify what kind of "drops".
Shaking head could certainly be due to ear infection, though, as could wobbly walk. However, kidney failure will also cause a backlog of "toxins" in the bloodstream and this will often make animals feel very sick and wobbly. And then there's a myriad other "neurologic" possibilities in there, too, but the above issues would be most common.
Kitties in failure usually have really stinky breath. Owner doesn't mention this.
Unfortunately medicine is often a guessing game, even in humans. It might be really difficult to find out what's going on with any given patient, and sometimes all you can do is treat the symptoms.
Anyway, have to be a little political on this, as I can't go overboard on diagnosing without seeing the patient. Would be interested in knowing what the rest of the bloodwork looked like, what they found in the ears (mites? bacteria? yeast?), is she showing any other subtle neurologic signs? Blahdeblah.
Good luck to her. I would recheck with vet if not doing much better in another day or two. Kitty needs to eat -- SOON, or she may risk dealing with liver issues soon, too.