The actress played the ill-fated vampire Rose, who after being bitten by a werewolf, was ultimately staked by Damon (Ian Somerhalder) in order to spare her from the agony of death.
She spoke to Entertainment Weekly about her departure from the CW series, admitting that she cried when she first read the script.
"So dramatic," said Cohan. "It's not usually what you expect to get to do when you're guest starring on a TV show. I just thought it was such a moving script. First and foremost, she's in that dream sequence, and she's just so happy."
She continued: "She's overwhelmed by that, and then realising why [Damon] was doing it… The peace of knowing that he was making those last moments enjoyable and just letting herself enjoy it."
Cohan will next be seen on Chuck, where she plays a young English heiress named Vivian McArthur who comes to Chuck looking for help.