Well, don't know what to say really. She is still here but I sort of got the impression that if I had said today to put her to sleep they would have done. She has no infection they can see and I am not willing to put her through a barrage of tests to find out what I already know, which is that she is getting senile. I explained that she has snapped a couple of times and that she is starting to piddle and poo wherever she is and the vet said that all they could do really is give medication if she is dribbling where she sits but not if she has control but just doesn't bother about asking to go out. Her heart murmur is markedly worse than it was in May last year but not yet bad enough to cause coughing but I have to look out for that too.
I was really just told that she is now on the homeward journey and when (along that journey) I decided to say goodbye was up to me. The way I see it is that she has caused no damage with her snapping yet. She isn't in any pain and her pooping isn't bothering me overly much so I will just go with this day by day. If I think she has had enough then I will let her go, with no regrets.
Thank you everyone for all your concern.