It's so hard when our dogs age and begin to decline. I recently lost my 3rd. Borzoi to cancer at age 9 so I know what you're going through.
Our vet said baby meat jar food would get her appetite back and it did for awhile but eventually the pain was so bad that even high dose pain meds didn't touch it and we had to say goodbye.
Best of luck with your beautiful "baby". We never have them long enough it seems.