With friends like Tia, who needs enemies? Antoinette first meets Tia when Tia followed her home, hurling racist insults at her – the basis for a sound friendship, right? Of course not. While they do become friends, the friendship quickly shatters over a petty bet and they go back to hurling racist insults at each other. But, in the last scene at Coulibri, we never see Tia actually throw the rock that hurts Antoinette, either because Antoinette has repressed that memory (it's her point of view in the narrative) or because the novel wants there to be the slim chance that someone else threw the rock.
For Antoinette, Tia is the image of someone who is completely in tune with the island and with her black community in a way that Antoinette could never be, however much she desires it. Antoinette's constant reference to Tia as her reflection, even in the last dream at Thornfield Hall, suggests that her desire for the wholeness that Tia represents is a driving force in her life.