Who does Rivka say they can fool if they follow the rules in The Devil's Arithmetic?

In The Devil’s Arithmetic by Jane Yolen, young Hannah is transported back in time to a concentration camp during the Holocaust in Eastern Europe. While there, Hannah meets and befriends another young girl named Rivka, who is actually Hannah’s aunt in the present day—although she doesn’t know this fact until much later.
Rivka is responsible for showing Hannah and her group how to survive in the concentration camp, including what rules to follow in order to minimize their chances of being sent to the gas chamber.
The answer to this question comes in chapter 14, when Rivka explains that they will fool the “Angel of Death” if they play by her rules. This is a metaphor, of course, for death itself, but could also be discussing the lines in which certain prisoners were selected for the gas chambers, in which a Nazi officer or doctor (such as the famed Dr. Mengele) would be in charge of making such decisions.
The rules, according to Rivka, include some of the following:
Don’t hang around or congregate in places with Greek Jews because their language barrier often makes them targets for punishment; those in close proximity often face punishment by association
Let people who do not want to follow the rules go their separate ways
Avoid the doors to the smokestack, which Rivka calls Lilith’s Cave
Hide in the garbage dump, known as the midden, when Commandant Brauer visits the camp, as children under a certain age are not supposed to be there
Rivka has been at the camp for some time when Hannah arrives, and she proves herself to be knowledgeable about what it takes to survive in such a horrific place.
Of course, Hannah ultimately sacrifices herself in order to save Rivka from the Angel of Death, before she is transported back to the present day to have dinner with her family in New Rochelle.