How can a client be prosecuted for extortion when the client's attorney did the actual extorting?

Extortion is obtaining of property from another induced by wrongful use of actual or threatened force, violence or fear, none is which has anything to do with anything in your story. This woman supposedly gets raped and then allows nude photos to be taken after the rape and has sex with her attorney in exchange for his services. This isn't the male world against poor Karen. This is probably Karen trying to extort money from the "rapist" she had sex with in exchange for her keeping her mouth shut about it. If she was wrongly convicted she should be working on her appeal.