Sin was originally chosen to be the next
in case she died, where she went through strenuous training to prepare her for the role.
When Black Canary traded places with Lady Shiva, Lady Shiva went to America and Black Canary travelled to the place where Lady Shiva currently resided and trained. There, Sin met Black Canary and the both of them instantly formed a bond. Black Canary then grew tired of the training given by Mother, the woman who was in charge of training Black Canary, and defeated Mother, and travelled back to America, where she brought Sin along with her. In America, Sin learned how to speak English and the Western world. Black Canary raising Sin was a handful, so Black Canary decided to leave the Birds of Prey, though changed once she joined the JLA.
Major Story Arcs
Brightest Day: Birds of Prey
For more information see Brightest Day
Sin is kidnapped along with her foster parents by White Canary and taken to Bangkok, to be used as hostages to force Black Canary into fighting Lady Shiva. Huntress (Bertinelli) takes Black Canary's place and give Black Canary time to find Sin and rescue her, sender her back to the states safely.
Powers and Abilities
Sin is very proficient in hand-to-hand combat considering her age and her small stature, taking down (about) five trained special agents to give an idea, though her full abilities in hand-to-hand combat is not known. She is also highly proficient in the Pokemon trading card game.
Sin appears in Arrow a girl (in her teens or 20s) who is saved and taken in by a female vigilante. She does not seem to have any ties to the League of Assassins, but the female vigilante does. Sin's actual name is revealed to be Cindy.