Please accept my condolences on the loss of your sweet Lucy Lou I had to have my Abby put down just this past June, so I know how hard it is to say goodbye to a beloved cat. In Abby's case I think the decision was a bit harder....she wasn't in acute pain like Lucy was, but she had bladder stones and diarrhea and the vet had done all he could for her.
I still wonder if the decision I made was the right one.....I think this is something all pet owners go through. Your emotions tell you one thing but your intellect says another. In this case, go with your intellect...you made the right decision about Lucy.