Min this is horrible for your friend and her family, I have never heard of a vet suggesting this when a dog still has a quality of life, if he was of his food, and in discomfort or not standing etc then yes but it is a heck on a thing to suggest.
I assume he can feel a mass and his tummy is distended. As for the passing of blood, maybe he is preparing her for the worst! Does Bertie get distressed and pant when he poops, if this is the case and distressing and he is in pain, I think I would ask a lot of questions before I make a decision
But regardless of that I send caring thoughts to your friend and her Bertie, and that every day he is with her he is special and loved and may there be many good days