Jim C. Hines wrote an insightful piece titled "Writing About Rape" for Apex Magazine.
I commend this article to your attention. It's a very interesting read. Here's an excerpt:
So you’ve decided to add a rape scene to your story. After all, you’re writing a horror story, and what’s more horrific than rape? It’s the perfect way to show how evil your villain or monster really is, and everyone always says you have to start a story with action and conflict, right? Best of all, your story will help to educate women about the dangers of walking alone at night! The editor is a chick, so she should appreciate that kind of thing.
I admit this is a hot-button issue for me. I’ve worked as a rape counselor and spent several years speaking to various groups at my university about sexual assault issues. I’m also an author. So reading books and stories where the author added a rape to make things “edgier,” or to motivate the heroine, or simply because he or she didn’t know what else to do to that character–it gets old fast.
Story after story in which rape is a quick, thoughtless way to motivate a woman to set off in search of revenge (“Red Sonja Syndrome”), or else it’s lazy shorthand to show how evil someone is, like having them kick a puppy. Or worse, it’s written in such a way that the writer seems to be reveling in the act him- or herself, glorifying and celebrating every graphic detail.
If you’re going to write, write thoughtfully. Write with knowledge and understanding.