Michelle Christine 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 (Buffy the Vampire Slayer (TV series)) for the shows final three seasons, Penny in the 1999 film adaptation of Inspector Gadget (Inspector Gadget (film)), Wendy in Mysterious Skin, and Harriet M. Welsch in Harriet the Spy (Harriet the Spy (film)). Trachtenberg also appeared on House (House (TV series)) and played Georgina Sparks in Gossip Girl (Gossip Girl (TV series)), and recently co-starred in the movie 17 Again (17 Again (film)), as Maggie. She also appeared in the 2009 NBC television drama Mercy (Mercy (TV series)).