To have a claim under the EEO statutes the individual must have suffered actionable harm. While there has been great debate as to what constitutes harm under the statutes, the problem with the situation you describe is that the victim hasn't suffered any harm under any of the viable definitions of harm.
That the harasser is bad mouthing her to the employer, quite simply is not actionable harm. No body has done anything to her. The harasser hasn't said anything to the victim, and while the harasser has made comments to the employer, the employer hasn't done anything to the victim. It's not even clear from your descriptions, that the victim is even aware that the harasser is making comments about her to the employer. A knowledgeable employer, listening to the harasser bad mouth the victim, contrary to your recitation of facts, would know that the harasser isn't engaging in illegal retaliation.
In the EEO area, name calling, even using derogatory terms, does not automatically rise to the level of actionable harm. The law looks at the severity of the action and how often it happens. If the harasser called the victim a lying bitch to her face in the middle of the work place, that single statement would not be sufficient to rise to the level of actionable harm under current interpretations of the EEO statutes. None of this means, however, that an employer can't prohibit uncivil behavior or lying or however it would describe your revengeful actions of the harasser. The only point I'm making is that the harasser's actions don't rise to the level of illegal retaliation.
In response to one of the other posters, I'm not proporting to be anything. I am simply trying to share some of the knowledge I've gained while doing this work for thirty years. I have nothing to gain by trying to deliberately mislead anyone. My standard advice to anyone who describes an actual situation, whose facts lead me to believe that there might be a violation of any of the federal EEO statutes, is to contact EEOC or a state or local human rights agency for further information and guidance. I typically don't recommend attorneys unless I know their qualifications and experience.