Why does Anja feel guilt over the death of Richieu in Maus 1 and 2?

Anja feels guilt over Richieu's death because she and Vladek made the decision to send him to Uncle Persis in 1943, believing he's be safer there. When Zawiercie is liquidated, Tosha poisons both herself and the children in her care in order to save them from the horrors of the gas chamber. Anja will never forgive herself for sending Richieu away and into danger. She feels responsible for his death.