The Question and Answer section for The Silver Sword is a great resource to ask questions, find answers, and discuss the novel.
Ivan is a Russian sentry at the outpost in Warsaw. She gives Ivan a lesson in hospitality when she invites him in for birthday tea.
In Chapter Nine, Ivan does display persistance. He is able to obtain the supplies Ruth requested, and he has also located Ruth's brother, Edek, and is willing to go and find him.
Of all the novel's characters, Ruth Balicki best fits the description you've provided.