Who is Calinda from The River Between Us and what is their importance?

Calinda arrives on the ship from New Orleans with Delphine, and when Tilly first sees her, Calinda appears to be a servant, perhaps even a slave. Over the course of the narrative, however, Calinda is revealed to be Delphine's sister. She is friend and confidante to Delphine and to Cass, but eventually chooses to leave for California where, as Tilly tells Howard in Chapter 15, she could hopefully pass as Hispanic, escaping the racism-defined constrictions and conditions of her life.