Who is Ruth from Enchantment and what is their importance?

Ruth is a young Jewish girl and Ivan's fiance. Ivan feels disloyal to Ruth when he wakes Katerina, but he overcomes his guilt by telling himself that Ruth is not even born on the day he becomes engaged and marries Katerina. Ivan later humiliates Ruth by telling her of his marriage to Katerina in an airport. Ruth is later used by Baba Yaga in a murder attempt against Ivan.