Stefanie Gates works as a social worker inside Leonida's Department of Corrections, the state prison that appears early in GTA 6. Rockstar gave her the distinction of being the first voice players hear in the game, opening Trailer 1 before any picture appears on screen. In that opening scene she is shown in her office talking with Lucia, who is behind bars at the time, setting up Lucia's story before the player even reaches Vice City. The scene plays as calm and procedural rather than dramatic, given her job title. What happens between her and Lucia after that scene, and whether Stefanie plays any further part once the story moves past the prison, has not been detailed. Rockstar has left that thread open.
The community companion for Grand Theft Auto VI. Database, maps, guides and tools for Vice City and the state of Leonida.