Knowing when the right time is, is so hard. We lost our Pippin after 14 years of wonderful adventures. Our newer Yorkies will never replace him, as I'm sure you agree, each dog we love is unique in personality just as we are.
Anyway, when the vet you trust says there is nothing more that can reasonably be done, that is the time.
When they don’t want to eat any more, (even baby food), and cant control their pee and poop, and eventually can't even stand up by themselves, it seems obvious. Still, it was the hardest day in my life when we had to say goodbye to our first Yorkie, who had all those symptoms.
Queenie knows you love her, and that you will make the best decission.