UPDATE: Sweetie is doing great!
Sweetie and Mark Twain have something in common (besides being long-legged and witty). My expectation of her imminent demise was (so far) premature. 
@thorny_locust, I can’t thank you enough for your post of Feb 23 where you suggested I get her nails trimmed. What a clueless mom I was! 
Her rally started after the nail trim, and she has improved steadily-- I mean, up to a point, of course. She’s not turning back the clock, but decline has leveled off to sort of a plateau.
She’s eating heartily (although not putting on weight), she is walking like an old doggie-- heck, like an old person–, getting up and down with effort, coming to me on schedule for her pills, wagging her tail and showing a doggie-smile when I fuss over her. She hasn’t had any accidents in the house, God bless her. When we all get up in the morning (around 5 or 6 am) she immediately heads for the back door to go out. She has fallen a couple of times when she manages to find the few square inches of floor that are not covered by yoga mats.
Turns out the clumping-fur-loss thing is something normal that happens to dogs in the spring. It had never happened to her before, but I had a groomer come to the house on the weekend to brush her out with a de-shedding brush and now she looks all tidy and well-groomed again. If I could figure out how, we could have made a new puppy out of all the brushed-out fur. Now that I’ve seen it done, I think I can do it myself.
She spends 85% of her time sleeping, but gets up regularly to eat and go outside. AND she comes to me to let me know when her food bowl is empty – some days she will eat 2-3 bowls of food, other days not so much. (Rotisserie chicken, pot roast, high-quality beef/chicken dog food, hard cooked eggs, cottage cheese.) Eating, sleeping, pooping – hey, it’s a life. Throw in an occasional TV binge or a good novel and that could be me. And probably will be me eventually. If only I could find someone to wait on me like I wait on her.
Damn, I love that doggie! 
Thanks, y’all, for your informative support. I’ll be back as time goes on…