I don't have personal experience with stage 4 kidney failure in a dog. I hope others here might comment to advise also.
But my advice is this.
Bless her Soul. I think you should face that she doesn't have very long for this world. She might beat the vet's estimation. Who knows? She might have more weeks, or she might pass in less time. Sometimes they can surprise us.
Now so long as you are seeing no signs of discomfort, inability to eat and drink, vomiting, or other signs of distress....I would say that the kindest thing is to treat her with gentleness, kindness, and great vigilance. Going out for long periods of time will not be a good idea. Can you manage that? She is now in a "Hospice care at home" scenario.
Slowing down, or any other changes are acceptable. Being unable to eat, relax, sleep, have any enjoyment of life, hold down food, drink water, or slowly potter about the garden are not good signs. If she can do all those things, she is slowly letting go of the world in her own time, and that is okay. There is nothing cruel or wrong in a dog living out its last days/weeks in hospice care.....so long as there is no pain and suffering.
A sure sign of pain in dogs is -unwillingness to move, refusal to eat (usually), shivering, and only sometimes, whining sounds.
But keep a very close eye on her for any negative changes. You are her guardian and her nurse now, and she depends on you to relieve her of any suffering which may eventually happen.
"Palliative care" medications may help very much. You can speak to your vet about that. Some vets don't agree with the hospice care idea, and prefer to euthanise a.s.a.p. It is possible that's because they don't trust the animal's caretaker to make brave and selfless decisions, or to be aware when it is "time".
But it is up to your dog, and how she is.
This is a tremendous responsibility for you. But with real love and careful management, those last days can be very sweet.
My kindest thoughts to you both.