The Evil Fingers used to be a teen girl rock band, and is now a group of friends, which includes Cilla Norén.
Mimmi is not a member, but Salander does introduce her to the Evil Fingers. We don't meet the other members. Salander considers turning to the Evil Fingers after Nils Bjurman forces her to perform oral sex on him in his office. But she doesn't want to reveal to her friends that she's a ward of the court and is considered mentally ill.