From WENN.com

The Scream star will play one of his character Dr. Derek Shepherd's four sisters in two episodes that will air in the U.S. in December (12), according to TVGuide.com.

Embeth Davitz and Caterina Scorsone have appeared as Shepherd's siblings in previous episodes.

Campbell's latest TV role will be a reunion of sorts - she and Dempsey co-starred in Scream 3.