Question about Cat's Kidney Failure?

I had a cat who's kidney's were failing she was a stray when i took her in, the vet put her age at about 18 years when her kidney's started to fail, i didn't see any blood, but she had a terrible thirst and got very weak she was put on antibiotics which helped for a while but she went down hill very quickly over night ,she couldn't get up, and even went for a wee where she was led down. I took her to the vet and was told she was suffering and it would be kinder to have her put to sleep, it broke my heart but it was also upsetting to see her suffer, and the constant trips to the vets was also very stressful for her.I do know what your going through.