In the Charles Bronson movie Kinjite: Forbidden Subjects, there's a female pedophile (and her role is actually billed as "lesbian pedophile" just to clear up any confusion) portrayed (fairly negatively, as it was an 80s exploitation action film, but interesting nevertheless). There was also sex between an adult lesbian and a 14 year old girl more positively portrayed in The Vagina Monologues. Those are the two I can think of off the top of my head, but there might be more. But you're right, it is rarely portrayed in the media. The real life case of the Hispanic woman in Southern California who exposed her female teacher for molesting her as a young student has sort of brought it out in the open somewhat. Previous cases in the news had usually involved female teachers with male students.