Following her much talked-about guest stint on the series Weeds, Mary-Kate Olsen is turning up on an episode of Samantha Who?. The actress plays a self-destructive bad girl who reminds Samantha (played by Christina Applegate) of herself at a younger age. The show's producers raved about Mary-Kate's professionalism. "She showed up alone, ready to work, is great on the set and is serious about the job," says Don Todd. "She's smart and she knows what she's doing." Mary-Kate can also be seen opposite Ben Kingsley in the film The Wackness, which comes out on July 3.