who else in chapter 21 can be seen as "a bird who flies" and why?

That would be Ruth. Dennis called her to say that Mameh had passed away. It took a long time for Ruth to pull herself out of her grief. Dennis told her that she had to forgive herself, and Ruth knew that her mother had given her the passport because she had been aware that she was dying. Dennis talked to her about God, and said that she would be forgiven. She started going to the Metropolitan Church in Harlem, where Reverend Brown was the well-loved minister. Ruth says, "that's when I started to become a Christian and the Jew in me began to die." She then describes an incident when Mameh was waving a live chicken over her head, and told Ruth that death to the chicken would give her life, and that a bird that wasn't able to fly wasn't special anyway.