oh Margaret I'm so sorry to hear this dreadful news.
Just wanted you to know that I'm thinking of you and Gizmo - we're all here for you.
I'm sure you will know when it's time - if possible, ask your vet to come out to your house - I think the dog is calmer in their own home. I know it's really hard but the kindest thing you can do is to be with them at the end.
Maybe have some of Gizmo's favourite treats prepared - we gave Peaches some prawns, her favourite, and she was so busy concentrating on those she wasn't aware of what the vet was doing...
Thinking of you and sending comforting thoughts, and wishes for a peaceful parting when it is time.