Phill, my last rabbit Little Happy was diagnosed w/ chronic kidney failure. Although there were conflicting view btwn. 2 bunny vet specialist. With him, only 1 kidney is failing.
Does Tilly fur feels dry? How old is she? Is it one or both kidney failing?
In the end, Little Happy passed away due to liver cancer, so the chronic kidney failure never got to him.
I notice Little Happy always sit at a certain spot in the house, and won't pee until he really needs to. And to make matter worse, the litter box was upstair and he is too lazy to run upstair to use it.
So since I discover the problem, I took him to the litter box once every 2 hr., regardless whether he needed to pee or not. This is important, as it prolong the lifespan of kidney.
I can't see any rabbit's kidney need to hold urine for so many hours, as it is like using their kidney in overdrive mode.
With my current bunny Goofball, she does the same thing as Little Happy, sits at a spot for hours (say night time when we are both asleep), and didn't bother go to any of the urine spots.
So what I did is whenever I need to use the bathroom or wake up in the middle of the night, and in my case, it's about once every 2 hr., I'll grab her to her favorite pee spot, leave a towel that I used to clean the previous urine spots at that same location, this towel clearly stinks with the urine smell, and she'll smell that towel and encourage her to pee.
And i notice what comes out isn't a large spot. In other words, her kidney wasn't full. So "Induce Peeing" is a great technique for rabbits with healthy kidney or chronic kidney failure. As I totally disagree w/ the way these rabbits hold on to their urine inside, and won't pee until it's abs. necessary. I mean, human doesn't do that, doing so would to a test of kidney strength, and I see no reason any human or animal should do that.
With Little Happy, my vet said they can live a happy life even w/ chronic kidney failure, with the proper care. Try the above technique, it works very well for me for my indoor house rabbit.