Sue I'm so sorry to read about the little rescued corn and the tumour. I can't offer you any words other than support and care during this tough time. As Christie said, write your questions out before the vet visit as it may be a stress filled time for you. Trust yourself to make the best, most humane decision for this snake with the advice of your vet and you'll do what is best, I'm very sure of that.
Our thoughts are with you dear.
~~Jo~~