Michelle Trachtenberg (born October 11, 1985) is an American television and film actress. She is perhaps best known for playing Dawn Summers in the television series Buffy the Vampire Slayer for the show's final three seasons, Penny in the 1999 film adaptation of Inspector Gadget, and Harriet M. Welsch in Harriet the Spy. Trachtenberg also appeared on House and played Georgina Sparks in Gossip Girl, and recently co-starred in the movie 17 Again, as Maggie. Michelle Trachtenberg is currently one of the stars in the fall 2009 NBC drama Mercy.