Katie Cassidy

Film Deaths:

When a Stranger Calls (2006) [Tiffany]: Strangled to death (off-screen) by Tommy Flanagan in the woods outside the house; her body is shown afterwards when Camilla Belle discovers her in the bathroom.
Taken (2008) [Amanda]: Injected with an overdose of heroin (off-screen) by Arben Bajraktaraj; her body is shown afterwards when Liam Neeson discovers her.
A Nightmare on Elm Street (2010) [Kris Fowles]: Slashed across the chest by Jackie Earle Haley in her dream (causing her to be thrown around the room and slashed in the real world as well), as Thomas Dekker looks on in horror (see also Amanda Wyss' death in the original film).
Wolves at the Door (2016) [Sharon Tate]:

Harper's Island: Gasp (2009) [Trish Wellington]: Stabbed in the stomach by Christopher Gorham.
Arrow: Legends of Yesterday (2015) [Laurel Lance]: Vaporized (along with Emily Bett Rickards, Danielle Panabaker and David Ramsey) when Casper Crump causes a megablast from the Staff of Horus (This timeline is altered, however, due to Grant Gustin running fast enough to go back to the previous day, so Katie survives the episode).
Arrow: Eleven-Fifty-Nine (2016) [Laurel Lance]: Dies in the hospital after being stabbed previously in the stomach with an arrow by Neal McDonough as Stephen Amell, David Ramsey, Willa Holland and Emily Bett Rickards look on. (Starting with the fifth season, Katie begins appearing as Laurel's Earth-2 doppelganger, Black Siren though she also appeared as Black Siren in the second season of The Flash.)