Not much is known about her past, except that she had suggested that her parents may have regretted having her or consider her to be dead.
In "Broken Dolls", Roy Harper was directed in her direction when looking for The Canary. When asked about her and led him to The Canary's hideout, and she knocked him out. When he woke, she looked on as he was questioned by The Canary, but she let him go when The Canary told her he was harmless.
In "Crucible", she shares breakfast with The Canary who is revealed to be Sara Lance, they both talk about their families. She later encounters Roy again and meets Thea, she mentions to him how Thea doesn't know about him being the Arrow's sidekick. When The Mayor attacks the event they are at, she is wounded and is saved by Roy and Thea. She is recuperating at a hospital and is looked over by Roy and Thea. She wakes up later and says that because Roy saved her, she will keep his secret. She comments to Thea how Roy is an idiot and Thea agrees and Sin admits to Roy that she likes Thea.
- In the comics, Sin is much younger; she is a child who was destined to become the next Lady Shiva, but she was adopted by Dinah Lance and Oliver Queen.