If your roommate has a regular access to your car, you should definitely include her name in your policy. As you never know when the accident is going to happen, it’s always safer to do so beforehand. Also, it can be a great way to save you money if you can share the auto insurance premium with your roommate. Learn more about adding someone to your policy by checking this article.
The information in this answer is general in nature and is not legal or insurance advice for your specific situation. Policy language varies carrier by carrier; your declarations page is the final word. If you're unsure, call your agent before you need to file.