Being raped means losing all power and control over what happens to her body. Restoring decision-making power to her as quickly as possible will help her heal. That means that she gets to decide whether or not to report the rape to the police, and she gets to make the choices about medical care. Let her decide whom else to tell. Don't increase her feelings of loss of control by telling anyone else without her permission.
Rape is an invasion of privacy-don't perpetuate that invasion.
Offer to go with her to the police, hospital, or sexual assault crisis center. Remember, don't pressure her to do something she does not want to do. Listen to her. It's more important that you let her talk about her feelings and how she perceived the assault than for you to ask questions about what the assailant did. Don't tell her to forget.