Arrow’s Katie Cassidy guest stars on the May 17 episode of The Flash.
“But wait!” you say. “Didn’t her character die?”
Yes, but she didn’t die on Earth 2, where Dinah Laurel Lance has the alias of Black Siren!
Here’s the official description from The CW:
KATIE CASSIDY GUEST STARS AS BLACK SIREN – After Zoom (guest star Teddy Sears) unleashes an army of Earth-2 meta-humans on Central City, Barry (Grant Gustin) is shaken when he sees their leader is the Black Canary’s Earth-2 doppelganger, the Black Siren (guest star Katie Cassidy). Meanwhile, Wally (Keiynan Lonsdale) takes to the streets to help The Flash stop the meta-humans, which worries Joe (Jesse L. Martin). Iris (Candice Patton) and Henry (guest star John Wesley Shipp) are concerned about Barry taking on Zoom. Jesse Warn directed the episode with story by Greg Berlanti & Andrew Kreisberg and teleplay by Brooke Roberts & David Kob (FL222). Original airdate 5/17/2016.