
I was so sorry to read your post, you must feel so sad :(
As you are asking the question you must feel that the time is near, although I think if I were you I would speak to the vet first just for their opinion on her quality of life.
Having said that, you know your girl better than anyone, and only you will know when it is time, and even then you will doubt yourself and wonder whether or not you have done the right thing. It is the last kindness or gesture of love we can give to our dogs, to put an end to their suffering, but is also one of the hardest and painful decisions you will have to make for her. I think someone said on here a while ago that if your dog loses their appetite, their desire to go for a walk or doesn't want affection then their quality of life is not good, and it is best to make the decision a little too early than a little too late.
I really feel for you as it is an awful time, but I'm sure you will make the right decision for your girl. I think most of us on this forum know exactly what you are going through and how you are feeling, unfortunatley there is no easy answer or anything I can say that will help make it easier for you.