Personally, I find the Ke$ha songs pretty funny. While not full on Rock, or entirely GIRL ROCK, might I suggest Vixy and Tony and Seanan McGuire for a well rounded musical experience? She'll LOVE 'Siren Song', and will get some food for thought from 'Wicked Girls'.

Joan Jett is definitely one of the Godmothers of Rock-N-Roll Girl Power.