What you need to do is be there for her as a friend. It's going to be a long, long time before she can trust enough again to let people close to her. The healing process after such a traumatic event may take years, and she will probably snap at you and push you away. But if you truly care, take her hits and comfort her when she needs you. It's a mark of your friendship that you asked how to help.

<Webmaster's Note: The rest of Duamerthrax's response contains extremely graphic depictions of violence. For the protection of more sensitive readers, we have printed this text in a masked font. Simply highlight the text to make it visible.>

As for the rapist: kill him. I'm not joking. Kill him. The rich have always taken what they wanted because they feel entitled to it. That's how the rapist felt about your friend; she had something he wanted, so he took it. We know how to treat people like that down here. Kill him.

Don't be stupid about it; plan it out to the smallest detail. Crime statistic show that most people can get away with a well planned crime once. Get a group of vengeful anti-rapists together, cover your hands and faces, and abduct him when he's alone. Don't speak, so your voices can't be identified. Take him to a remote, unvisited area and kill him.

Stab him in the lungs so he can't scream, but not so deep that he'll drown quickly in his own blood; he deserves prolongued torture. Next, break his teeth with a sledgehammer, so dental records will be harder to reconstruct. Cut off his genitals with a hacksaw, stuff them in his mouth, and sew his lips shut with barbed wire. Then tie each of his limbs to stakes, pound them in the ground, douse him in kerosene, and set him on fire. His last few moments of life will prepare him for his afterlife down here.

I'm sure you're wondering why I'm advocating hideous violence. It's simple--profit. The rapist is coming to Hell, no doubt about it. But if you kill him, we get two souls instead of one.