<p>Everyone seems to be sticking to authors, so I suppose I'll represent the musicians. This might be the way to go for your daughter; she won't have to read things; instead she can listen to songs that are catchy, easy to remember and easy to get a feel for.</p>
<p>Rage Against the Machine - super political band with a lot to say about the state of the world. Very left-leaning, but then, most of these are.
Bob Dylan - obvious choice here, he wrote some amazingly political songs about Vietnam, socialism, loss of American innocence. Good stuff. Other similar ones could be Joan Baez, the Mamas and the Papas, John Lennon & Yoko Ono, etc.
The Smiths - just have to throw this one out there. Morrissey's lyrics contain a lot of leftist social commentary, about things as varied as homosexuality, anarchy, poverty, crime, etc.
James Brown - father of "I'm Black and I'm Proud", played a significant role in the social validity of the civil rights movement in the 1960s.
The Sex Pistols - promoters of anarchy and the social punk movement in the 70s.
Elton John - his huge popularity and success were a pretty huge stepping stone to the cultural acceptance of homosexuals in society.
The Ramones - pioneers of American punk rock.
The Beatles - influenced a generation of Americans and Brits to do LSD.</p>
<p>Some authors she might want to try:
Thoreau or Emerson - leading Transcendentalists, very socially influential, but it may be a bit too heavy for your daughter, in which case may I suggest Allen Ginsburg. He was a poet in the 60's and his poetry inspired a lot of youth in America to protest the Vietnam War.</p>