Proposed Games: Arkham Origins, Arkham City, Arkham Knight
Within the comics, Stephanie Brown has assumed several identities. Before she had a shot at being Robin and then Batgirl, she was Spoiler. Angered by her father, the Cluemaster, returning to his life of crime, Stephanie took it upon herself to stop him by "spoiling" his plot through a series of elaborate clues. Though she's been in and out of the Batman Family, Stephanie was recently reintroduced in the New 52 back in her original role as the mysterious, but helpful Spoiler.
Though Cluemaster never appears in the Arkhamverse, he could have been incorporated as one of the assassins in Arkham Origins, serving as the inspiration for the pre-Riddler "Enigma" and giving a younger Stephanie the opportunity to counter her father's actions by leaving clues for Batman. She could make her first actual appearance as an ally in Arkham City, and then again in Arkham Knight. Between being mentored by Oracle and pursuing a relationship with Tim Drake, Arkhamverse's Spoiler could easily establish an actual place for herself within Batman Incorporated.