Poor old Girl.
Bess has served you well, so first off, dont feel guilty bout the decision. You want her to enjoy a quality of life, not an existence.
Not sure if you remember my Collie? I had to have him PTS just before xmas, because he was getting kidney failure. I had him nearly 13 years and was my best friend and loyal companion. He was PTS at the house, the vet charged £30ish quid. He is now buried under the living room window,
I remember the good, loyal friend that he was, not the pain he would have been in had I not have made the decision.