Speaking to TV Guide, Drew explained that the episode will surprise viewers.
"The finale is going to shock a lot of people," she said. "There's a lot of emotional stuff that happens between the characters that you love and the relationships that you love, that's going to turn things on its head."
Drew continued: "Something happens to my character that will change her future, for the next several seasons. It's very emotionally centred and emotionally grounded. It's not a big external thing that makes everybody freak out, but a lot of different characters are affected in this moment."
Grey's Anatomy's executive producer Shonda Rhimes has previously suggested that the finale will surprise fans, while Drew's co-star Owen McKidd has claimed that it will leave "big question marks".
Grey's Anatomy is expected to return for a new episode in the US on April 28 at 9/8c on ABC. The show continues in the UK on Wednesdays at 10pm on Sky Living.