TVLine reports that the actress will play Carol, the older sister of Lily (Kelly Rutherford), in a forthcoming episode.
The character will first appear in an episode scheduled for early April and could recur throughout the fourth season.
Douglas has previously played recurring roles on Law & Order: Special Victims Unit and Ugly Betty. She also recently signed up for a guest role on new NBC drama The Cape.
The role of Carol was previously played by Breaking Bad star Krysten Ritter in a flashback episode.
Gossip Girl returns to The CW on January 24.