In all seriousness, your roommate does need to be educated. But it may not be best if you are her teacher.
She probably doesn't even realize why her comment was inappropriate and even though it is blatantly obvious to you that doesn't mean you'll ever be able to help her understand. I'd suggest a diversity class that your school or local community center may be offering. And maybe you guys could take it together just so she realizes that it is important to you too!