So sorry you're facing this diagnosis. One point I'd make from my experience: unlike with human cancer patients, chemotherapy in dogs is not traumatic and sickening to the dog...at least this was the case with one of my basenjis who had brain cancer. The veterinary oncologist explained chemo is a different process in dogs. Jasper felt much better with chemo - the benefits were almost immediate - and his life was extended by a year.
I totally agree - don't prolong life if it's not good-quality life. Jasper had other medical issues including Fanconi, and the time came when he lost the will and energy to live. We didn't let him suffer. He just wound down. Rather than try to get him to eat, we had a vet come to the house to euthanize him. It was a peaceful death and Jasper was not afraid. He just drifted off to sleep in our arms. The other dogs were with us and didn't worry and search for him as sometimes happens when a dog leaves for the vet and doesn't return.
Another basenji, Keiko, had massive stomach cancer discovered during diagnostic surgery. She had started vomiting daily and the vet couldn't find a reason, hence the biopsy. We opted not to wake her up from anesthesia because there was no hope for good quality of life. Very traumatic for us, but not for her. We miss both of them terribly but at least we did all we could to give them a good life. Both were rescues.
My 11-year-old basenji female, Daphne, developed a persistent cough about 6 months ago. Tests were all negative. She wasn't exposed to other dogs, boarding situations, etc.
My vet prescribed Temaril-P...the 'P' stands for prednisone, which of course you don't want to use unless necessary, and in the lowest effective dose. I don't remember what the other components are, but the predisone is a very small proportion of the drug. It's given for allergies.
It's been very effective for Daphne. You first give a good dose for a week or two (sorry, can't remember exactly), then decrease until symptoms return to find the lowest dose. Hope you get to the bottom of this.
My 12-year-old basenji Daphne acted sluggish and depressed for about a year. Labs showed elevated liver enzymes (sorry; I don't have those values for you). We consulted an internal-medicine specialist who recommended ultrasound to rule out tumor or anything else that might show up visually on the liver.
Ultrasound showed nothing, and we've never learned what caused the abnormal lab values. The specialist prescribed a number of supplements to help her liver, as well as the medication Ursodiol. She's been gradually feeling better, at least by my observation, and her lab levels get better each time we test. Vet said to continue this medication and supplements indefinitely as they're nontoxic and seem to be helping.
Midway through all this she developed a dental abscess which we had surgically treated. The vet didn't know if whatever was brewing in her jaw might've stirred up her liver; we just don't have any idea what happened. This dental episode occurred midway along her gradually improving course, and cleaning out the abscess didn't change anything - except that Daphne's mouth didn't hurt anymore!
My suggestion would be to get your girl the ultrasound, since it's noninvasive and can rule out some scary scenarios. I wish I could be more helpful. If you'd like, I can list the supplements and dosages she's on. Best wishes to you both!