I'll start with a warning, this may read as though I'm uncaring and it's not meant that way at all, I've just been through the PTS process more times than I care to recall and it's never easy, but once the decision has been made its better for everyone involved to do it without procrastination and prolonging the agony of grief.
The OP has stated numerous times that the dog isn't in any pain but also that it has no quality of life, can't toilet independently or walk.
Allowing this situation to continue, especially as your vet has been talking to you for 6 months about putting the poor dog to sleep is, in my opinion, cruel, and I speak from having several similar experiences over the years with pets of my own.
No, we never want to have them put to sleep because we love them and don't want to have to grieve their loss but in situations where they are either in pain or can't do the most basic things independently it's in their best interests to end their suffering because that's exactly what is happening, pain or no pain, your dog is suffering because it can't do the basics unaided.
An 11yr old is plenty old enough to understand, especially when they've seen the dog on a daily basis and can see what it is going through.
Yes, there will be tears (I know only too well because I cried for several hours last night because my best friend's 12.5yr old cocker spaniel passed away at teatime), but it's best to tell your gd today, bring the vet appointment forward and end the suffering.
Some people on here have said about having the dog cremated and then burying the ashes, you could have the vet arrange to put them into a wooden box with the dog's name on it and give it to your gd or even a carved wooden dog to put on the mantlepiece, I've got the ashes of one of my cats who died in labour and her 13 (yes, thirteen) unborn kittens in a carved wooden cat.
It's going to be a very sad time in the run up to doing the deed and afterwards but there really is no point in delaying, there's nothing worse than sitting waiting for a pet to die, it's much better to accept it's going to happen, get it over with and not prolong anyone's agony for any longer than is absolutely necessary.