If you have finished the novel, you will know that Chaya/Hannah switches places, at the last minute, with Rivka and goes to her death in the ovens at the concentration camp, and she does this because she realizes that
"she lived, had lived, would live in the future -- she, or someone with whom she shared memories. But Rivka had only now."
This is the ultimate sacrifice for a friend! What more caring and empathic gesture could there be? This moment is poignant because the Hannah of the present day finally realizes why her Jewish name is Chaya -- her aunt Eva's Jewish name is Rivka. Rivka asked that her niece he named in memory of the friend who died in her place back in Poland in 1942, and to honor that sacrifice, she is remembered always.
Other places where Chaya is caring: giving extra food to the yougner children; running and helping to hide the younger children;trying to maintain a calm and rational attitude about the incredible circumstances they were all in and in that way helping everyone else cope too; trying to warn everyone of how devastating this holocaust was going to be for the Jewish people;