Very sorry for your loss. She's loved and you had great times with her. Our thoughts and hearts are with you.

I'm so very sorry about your Cassius and that you tried everything to find a diagnosis. It's always hard and we cherish the time we had with them. Our hearts and thoughts are with you.
It's good you posted about this condition as it may be helpful in case these symptoms show up in other doggies. And would definitely want to know the root cause.

Share your B's quirk or the one "thing" they are adamant they must and will do (and will not compromise on).
With my Casey, it's the walk - she must lead the walk. With my Cosmo, it's the bed - she must sleep on the bed and my presence is required. They're kinda well-behaved and they made me smile when they "insist" so I just let them be (and of course I took lots of photos).
What about your basenjis?

I think some doggies get dizzy or nauseous when they don't see the horizon.
With my Cosmo, I have a hefty seatbelt safety harness in the back seat she's tethered to. She then positions herself in the center in the back seat where she can see the view from the windshield between the two front seats.
Maybe it will help if she's high enough in the vehicle (i.e. her eye-level) where she can see through the windows.

Thank you for your kind words and support. I think talking about it helps with the healing and that we're not alone in this difficult time.

My sweet old pups Cosmo has peacefully crossed Rainbow Bridge from home and is now with her siblings Raven, Jasper and my first B, Casey. In her annual vet visit in July, she was diagnosed with early stage renal failure. Followed the vet's instructions and got her Azodyl and also shifted from Merricks/Orijen Senior to low protein diet (Purina NF). At first she ate it then won't touch it at all. Then the blood panel in September showed she was in late stage renal failure. Got more info and help from the forum and got her on Epakitin and subcutaneous fluids every other day. I think the fluid is the one that helped her feel so much better as she seems to perk up after each session. Called her showhandler for more suggestions and got her on some raw food, variety of ground meat, since she won't eat anything that she used to eat except some treats. I know she's hungry but can't seem to want the food so not sure if she's feeling nauseous but nevertheless, it's clear she is not her normal self. I used to feed her twice daily all her life but now I was hand-feeding her six times a day and she was trying her best to eat. We spent our last weeks together doing our usual early morning walks, going to the park, driving around town, going to Jack-in-the-Box drive-through as she loved eating the french fries on our way home, gave her treats like vanilla ice cream and the whole life pure turkey breast that is her absolute favorite. We just love our quiet times together and above all, each other's company. Since the day I picked her up in Virginia at the breeder 12 years ago, I tell her I love her - every single day. I cherished every minute with my Cosmo and I know she does, too. I miss her so much. My heart feels empty. My.heart.hurts. I love you always and forever, my sweet, sweet Cosmo.

Thank you all for your support, help and sharing your knowledge and experiences! It's feels better to know there are options that I can explore. Her quality of life is of utmost priority for me and want her to be comfortable and happy. She's curled up beside me right now on the sofa and snoring as I'm writing this.
(oh, her phosphorus level is 5.7 and last year, it was 5.0)

@tanza Thanks! When searching, I think those paid ADs are skewing the correct results when googling for holistic vets. So I dug in a little deeper and found the American Holistic Veterinary Medical Association and they have a VetFinder (yeahhh!). It turns out there's a Vet (in the same clinic as my Vet, but in a different location). This Vet has a "Whole Food Formulator" certification. I think I'll contact that Vet but hoping it won't be awkward. And will catch up with Tayda_Lenny and check on the posts.

@tanza Yeah, Cosmo sniffs the kidney diet food first and whatever smell it is, she just walks away (and then looks at me with disappointment). Any suggestions on holistic Vets?