Bessie, Bigger’s girlfriend, works so hard that all she wants on her day off is to get shmammered. Bigger wants a little loving and she’s willing to exchange sex for liquor money. Needless to say, this is not the healthiest relationship in the history of relationships.
But their arrangement works out pretty well... until Bigger gets his job and kills Mary. Then Bigger wants Bessie’s help to get money from the Daltons by pretending Mary’s been kidnapped. He doesn’t tell Bessie the real story, but Bessie is sharper than he bargains for and she figures out that he must have done something bad to Mary. (He's also acting uber-guilty.)
Bessie is way less than submissive to Bigger’s command that she help him. Then things go badly at the Daltons so Bigger tells her more than he intended. Her fear and remorse make her a liability and Bigger realizes he can’t leave her behind, but he also can't take her with him. He kills her.
However—ugh, this novel makes us so mad—since Bessie is black, Bigger isn’t put on trial for her murder. Ultimately, Bigger is arrested and sentenced to death for killing Mary. As a result, one of Bessie’s most important roles in the novel is to show the prejudice of the American justice system.