Chubby's dying

Her kidneys are failing. The vet said there is nothing that can be done, neither surgery nor medicine can fix cats. Her BUN levels and Creatinine levels are extremely high. She has always been very skinny, contrary to her name. But during last week her bones are really sticking out. She can't keep any food down, and since the weekend she is not even trying to eat. Even when I give her churu which she loves and always eats, she just takes a couple of licks and goes away and vomits it all up. Since yesterday water just seems to run through her. If she eats or drinks anything it comes up again within a few minutes. I was following her around with paper, wiping fluid bubbly vomit, and pink urine everywhere she went.
The doctor gave me some pills to cleanse the waste products in her body but it would be just a very temporary solution and her levels would rise back up again cause her kidneys are not working. I tried last night but it would mean force feeding her with something that I mix the medicine in. Even mixing with churu and using a syringe puts her through such discomfort and stress that it breaks my heart. I will at least save her the temporary medicine I want her to do what she wants.
I am so very sorry and very very sad. She is a tiny tiny fur bag with small bones in. She weighs 2 kg now. When she is not throwing up or peeing, she just curls up into a very very very small ball and covers her eyes from the light and tries to sleep.
She slept on top of the blankets in my bed as usual. This morning I noticed it was wet all over the bed blankets, where she had not been able to control herself (the vet injected quite a lot of water along with vitamins) and I had to find every spot and wipe it because the pee quickly gets cold and uncomfortable to sleep in. I also wiped her hind legs and butt because for the first time she had not the energy to do it herself. I think the bed is right now the most comfortable place for her. I brought another blanket and covered her where she was trying to sleep.
She is not eating, she is not drinking, she is really down to her bones and I think if not already, she will start suffering....soon.
I think I need to put her to sleep soon before that. She doesn't deserve any pain. I hate myself.
It is all so sudden, only this weekend she was out in the garden and running around and playing. I even encouraged and taught her how to climb the ladder from backyard to garden main area.