Currently in Chapter 3, Season 2, you can find Doctor Slone as an enemy at The Fortress. However, she was in different locations in past seasons and will likely change spots in later seasons, too. During her original appearance in the game in Chapter 2, Season 7, she was at Corny Complex in the underground base there. Then in Chapter 2, Season 8, she was at her base at the IO Staging Facility. Chapter 3, Season 1 is the only season so far that she skipped for some odd reason.