Hi,
If you have looked back at some of the other posts on this site you will see that I hold strong views about keeping pets alive when they no longer have an acceptable quality of life. Part of our responsibilty towards our pets is to save them from suffering, and we have the privilege of being able to do so when their suffering has destroyed any quality of life thay may have.
An animal's life span is so much shorter than ours, and we have to go through the trauma of parting with our cats and dogs several times over during our own lifetime. I always regard this as the price we have to pay in return for the love and companionship given to us by them.
With the signs you describe, togther with the vit's comment that he could feel a mass in her abdomen, I really think that the time has come when you will have to shoulder your responsibilty and consider sparing her further suffering.
W