Hello again, and thanks for your additional information.
At first, from your description, I thought maybe she had vestibular disease, a condition which affects equilibrium and is neurological in nature. It will cause a cat to walk like a drunkard, and not be able to keep her balance. This might also cause nausea, like when you're sea-sick, or have motion sickness, and this may be causing her lack of appetite. You can ask the vet if this may be a possibility. However, due to all the other symptoms you describe, it's possible that she had a stroke or a blood vessel burst in her brain, causing her glazed over look, and pressing her head against the wall.
If the x-rays revealed a mass in her kidney and her lungs are not clear, plus her urine is not being concentrated, which is probably due to her other physical conditions, she's not in good shape at all. At first, I thought perhaps if it were vestibular disease, it might run it's course with the help of some medication from the vet, to help her feel more comfortable. Then, I thought, perhaps a stroke, which may leave her slightly disabled, but not in pain and still able to enjoy quality of life, but unfortunately, from your description, I'm afraid I'm going to have to agree with the vet.
I know how difficult this is for you, but they say when a cat is no longer enjoying quality of life, which is defined as doing all the everyday things she normally does, then it's time to help her move on, so she's no longer suffering.
I wish I could make this easier for you or give you better news/hope, but due to all the things that seem to be going wrong in her body and perhaps also her brain, in my opinion, it would be best to let her go, peacefully.
My best thoughts and prayers are with you and your furry girl.