Rock music, by definition, should at some point, rock. It's one of those things which continually has its definition watered down by those who can't hang but want to. Margo Timmins? Wow.
As far as female rock vocalists who actually rock, Janis and Wendy O. Williams lead the way along with the likes of Patti Smith, Joan Jett, Kathleen Hanna, L7, The Beeders, Exene, Shonen Knife, Polly Styrene, Mia Zapata...