How do I bow out of this work situation gracefully?

I work for a small informal company. The office space I work in I share with my immediate supervisor and one other coworker. The coworker is my issue here. She will call her husband on the company phone line intentionally picking a fight with him for starters. What she does at home is none of my business and I don't care. But I have to sit in the same room with her listening to her yelling and cussing and slamming the phone when she's done. Not only that but if she happens to leave the room and come back in on the tail end of a conversation she automatically umes that you're talking about her and becomes irate and confrontational. (Ironically enough, up to this point the conversation is never been about her. Except for the one time we were discussing what we each were buying her for her birthday.) And as of yesterday, i found out that she's spreading rumors. I've been dealing with the other two issues for a while now and have been contemplating leaving my job becuase it's a stressful enough job without all the additional drama. Now learning that she's doing this now I KNOW it's time for me to leave. I've drawn up an e-mail to send to my immediate supervisor. But I know she's going to want to talk about it. I really like my boss and don't want to burn any bridges but I also don't feel confident in confiding the truth becuase my boss and the coworker have been friends for 10 years. I also am weary of what it will boil down to when the coworker finds out becuase she's going to know or at least ume my leaving is all about her and is going to get in my face. I don't like scenes and I want to leave as professionally as possible. But I can't be expected to stand there and take that. HELP! What do I do?