My Old Friend - When I need to let her go

Question
I love my 17 yr. old female lab.  I have had her since she was a pup.  She eats with great enthusium, drinks water as she has all her life.  She is pretty much blind and deaf ans has been for about 3 yrs, has an unbelievable number of moles, and a sore on her foot which she licks constantly licks and I repeatedly treat and bandage. I am very patient with her, have her on a pretty good schedule for going out- although she sometimes has an average of 5 "accidents" a week in the house- I keep the shampooer handy at all times.  I have other pets as well and she is somewhat tolerant of them- she just moves if she doesn't want them to be too close.  My issue is, I can't bring myself to voluntarily put her down just because she in sometimes inconvenient--having the thought of how much of a hardship life is on her- I guess I am also concerned that if this is all there is (life) that she should be here until she goes on her own and I have fulfilled her life as a friend and caretaker.  Please let me know your opinion on this topic.

Answer
This is a very tough decision.  We went through it with a 15 year old Lab last fall.  She had had cancer in her jaw most of a year.  Then she developed a huge tumor.  She quit eating and wouldn't even swallow pills in a ball of peanut butter.  Her walks had gotten shorter and shorter and she would just lay there and look at me when I took down the leash.  I knew it was time, she wasn't enjoying anything.  

Does your dog enjoy anything now except maybe eating?  Does she seem shamed by her accidents?  If she is still enjoying life, let her.  If not, no sense letting it go on.  Although our Lab was declining, she still enjoyed me taking her for a swim regularly last summer.