My question is, when do I know to let her go?
I love her to bits but now she cant enjoy her walks. She's happy at home and in the garden but what sort of life is that for her?I dare say you will just
know when the day comes. My old vet always used to say that there will be good days and bad days, and as long as the good days outnumber the bad, then it's fine. When the bad days outnumber the good, then it's time. At the same time, don't EVER feel guilty for taking the decision because being put to sleep means you KNOW your old and ill dog will not suffer, and "too soon" is only ever for you, never for the dog. The dog will not suffer if put to sleep, that is the one thing we know is 100 % true.
As for your above quote -if your dog is HAPPY staying at home, not in pain etc, then why not? My Cavalier rarely went for walks during his last few years of life. Perhaps once a month. I let him chose, all the time. When the leads came out he'd either appear or stay in his bed, so it was his choice. He was happy until the day before we let him go. Slept a lot, yes, fell over a lot too!, but tail always wagging, still wanting his food, still STEALING food when he could :) , still wanting to greet visitors and be included. He still had a life even if it wasn't the same life as he had as a youngster -but then what oldies (be it dogs or people) can have the exact same life forever? Not many.