How do Hannah and Shifre feel to have found a friend like Rivka?

You did provide an answer above. Rivka hands out bowls to the newcomers. She is resourceful and intelligent, quickly discerning how she may improve her chances of surviving day to day. Though younger than Hannah, she takes Hannah under her wing and shows her the ways of the camp. Hannah repays this kindness by sacrificing herself to save Rivka. Upon returning to New Rochelle in the present, Hannah learns that Rivka and Aunt Eva are the same person.