Why was Charlotte the only one to defend Zachariah against the Captian?

Zachariah and Charlotte are both exceptional among the Seahawk crew- one being a Black man and the other a girl. Zachariah stresses the importance of their getting to know each other and looking out for one another on ship because their respective differences put them at risk for mistreatment. Of all the people on board, Zachariah is really the only one who treats Charlotte with respect. Sure, the Captain speaks to her, but only in a way that builds up his own identity as a dominant force on board.
When Zachariah is about to be whipped as punishment for the crew's mutiny, Charlotte stands up for him as a friend. She is the only one to do so, however, perhaps because the other crew are thankful it is not them being whipped. As the only Black man on board, Zachariah is scapegoated because his life as regarded as less valuable than those of the white crew members. As a high-society girl, Charlotte has grown up with the institution of racial oppression, but she has no familiarity with it in a ship setting. I think that the foreignness of the ship's social structure makes her more free in challenging the Captain because she does not yet know what it means to violate those unspoken rules.