I don't think that monks need protection in the days after they die from anything, afterall they are monks. The story is from one of the monasteries in Athos, do you think they aren't going to heaven? And Theotokos was clear she said in the next life, not in the time they died before they enter heaven. And if they go to hell, she can't protect them, too. I think there is no hell and everyone evil together with the evil spirits live in one kingdom of the dead. So she is protecting them against other people in heaven and from the evil spirits and other armies that exists there. Also is possible to protect them from falling or sinning. And to keep them in good life in heaven.