Yes, sometimes we just have to let go of them. I did with my elder cats last year, and I cried a river, two.
But I like to fight diagnosis, so I believe you can prolong your dog`s life, make it good. First thing is the selenium content of the kibbles; if it is right; 0,8 mg of selenium per 120 gram (serving size)
that is a whopping 800 mcg per serving for a small dog, for a larger one, 3 times as much??
I would drop this food all together, unless they have done a mg / mcg mistake, happens quite often; or that the number should be 0,008mg. This happens often too..
I would give her raw food: cartilage, raw bones, raw fat. Liver and other tripe. As raw as possible.
Then add a "ton" of iodine, for a labrador 50-100 mg and no selenium if the listing of the food he has been given is right. Selenium has a loong half time, years, Iodine just 24 hours.
Then add borax, the bone fixer; also adress the fluoride, and the pain!. Used as a cancer remedy these days, boron.
Magnesium adress the bone pain as well.
Also; the homeopatic remedy Calcium Phos is a bone pain killer, you can give it daily in her water for the rest of her days.