Who is Rivka from The Devil's Arithmetic?

Rivka is a young, ten year old girl, who Hannah/Chaya befriends in the camp. Rivka is smart and calculating.... she has every intention of surviving the horror. Although Hannah/Chaya is the older of the two, it is Rivka who shows Hannah/Chaya the ropes. In the end, Chaya will give up her life to save Rivka's. At the end of the novel, Hannah discovers that Rivka is her Aunt Eva.