Normally, prior to the formal filing of complaint, the alleged victim seeks audience with HR to get advice on what to do. HR at this point, should explain the procedure and the likely scenario(s) once a complaint is filed. This is to ensure that the victim knows what to expect and is ready when the situation becomes ugly. Furthermore, HR should have guided the victim of her options, and likely groups that can help her legally if the situation calls for it. In this way, the complainant can get her thoughts together to make a decision.
While HR have its own biases, it should stay neutral and respect the rights of both the complainant and the one being complained. Remain objective but attend to the to the complaint and the victim, to shield the company from possible legal troubles.