Trachtenberg, 22, will play Georgina Sparks, a troublemaker from Serena�s (Blake Lively) past.
Mischa Barton reportedly turned down the role.
You just know there�s going to be a Blair (Leighton Meester) and Georgina showdown!!!
Michelle�s comeback career since 2003�s Buffy is certainly starting to take off! She�s also starring alongside teen heartthrob Zac Efron in 17 Again, out in August.