Susan Cushing was the eldest of the three Cushing sisters.
Her youngest sister, Mary, married Jim Browner, an alcoholic sailor. Due to the influence of the third and middle Cushing sister, Sarah, he later killed Mary and her lover, Alec Fairbairn, in a fit of jealousy and cut off an ear from each of them. He had meant to send them to Sarah, who used to lived with Susan, because he considered her to be the cause of the tragedy, but was unaware that she had moved to another place. The box, which was only addressed to 'S. Cushing', ended with Susan, who was disturbed by it and thought it was an evil joke.
It's most likely she was later informed of the truth, but it's not known how she took it.