In one slender documentary, co-directors Shane King and Arne Johnson accomplish what Hollywood routinely bungles: incisively depicting the inner lives of complicated young females. And they do it with the brio one would expect from a movie about the Rock 'n' Roll Camp for Girls, an intensive workshop in Portland, Oregon, whose campers spend five days learning how to play an instrument, write songs, and get along with their band members. (One of the counselors is Sleater-Kinney guitarist Carrie Brownstein.) The infectious energy dissipates somewhat as the filmmakers get sidetracked by data about the media assault on girls' self-images. Still, you've got to love eight-year-old misfit Amelia and her proposed opus, a 14-song cycle about her chihuahua (90 min.).