Teenage stepdaughter...need advice!!?

Ok Yahoo Answerers, I need advice!! I have a 13 year old stepdaughter. I have been with her father since she was 3, so it's not like I am "new" in the picture. Anyway, lately she has been sending me HORRIBLE emails, calling me evil, a b--ch, everything else. Her father confronted her and a told her this is not acceptable. She settled down and it seemed that she got over whatever it was causing it. The other night she left a screen up on the computer and it was her Facebook page. She posted a comment about her stepmom is the biggest b--ch, a stupid c--t, a fat cow, etc. How do I confront her on this??