why do so many people state "go to the police" as an immidiate response to all rape related threads, its not always that simple.
It might help for her to contact some of the rape crisis helplines, as they have people trained to help with this kind of thing, or perhaps a counseller who can help her talk through her problems. you might feel helpless now, but remember that for her to tell you took a lot, but also that she must consider you a good friend to be able to trust you, so don't doubt your capabilities as a friend. just be there for her as much as you can, and like you said you would, support her through this difficult time