As Linda asked, was the BLOOD glucose high as well? If so, she could be diabetic instead of Fanconi, or in addition to. As I'm sure you know now, high urine glucose with normal blood glucose is Fanconi, if both are high, think diabetes. We had a diabetic dog, drank a lot, peed a lot (with a dog door not so noticeable) and lost weight for months before we diagnosed it.
A dear friend recently discovered her girl has Fanconi. Like you, she noticed slow onset of symptoms and crankiness, but thought Fanconi was rare and had onset at about 5 years so had not been testing! (her girl is three). She has had a lot of contact with Dr. Gonto via e-mail. He has tons of knowledge to share but be aware, he scolded her rather fiercely about being so ignorant of her breed and of Fanconi. She understood that he is very passionate about this disease, so please understand that if he seems "less than sympathetic". She is working with 2 vets as well as Dr. Gonto to manage her girl, who has some 'normal' renal failure as well. My friend has beat herself up already (as you are doing) for not picking up on it sooner, she feels she may have had it for at least a year, looking back at events that were attributed to other things at the time.
So you see, you are not alone, if you have never been exposed to Fanconi, or only know about it as a "rare disease", you miss all these symptoms and don't put 2 and 2 together. Now you know, and I imagine you will educate every other basenji owner you ever meet. And you will do the best you can and hopefully you have more good years with your sweet girl. Try to just look forward and give yourself a break, you are doing the best you can and that is all anyone can ask of themselves!
Anne in Tampa