Carole, my RB Quasar had kidney failure, too. My vet told me to give her fluids three times a week and at first I couldn't do it. I couldn't stand to "hurt her" like that all the time.
But I did learn to do it because it made her feel so much better. And took it like a champ. But, Quasar had only one kidney from birth, so she did not last much longer even with the treatments. :(
Like Emeraldgreen said, if you use a very fine needle, I don't think it hurts much at all. In fact, it has to be very sharp, too. She never put up a fuss, which amazed me at first.
Good luck to you and Ash.