I like what Victoria said about It is your daughters choice. Keep it clean on facebook, or she cannot use it.. You can still take her computer privileges from her if she does not follow the rules. Tough cookies if she does not like it. She obviously is not aware of what she is doing for everyone to see.
The deal with facebook is that there are 3 different ways to use it. The open wall where all of her "facebookf friends" can see it. Real time chat, which only she and the person she is chatting with at that moment can see and the "send a message" which is like email where you send a private message.. Remind her to use the more private tools for her saucy or colorful language and conversations.
In our family, we are all on facebook, my mother, father, cousins, daughter, nieces nephews and we are about to do a page for our grandmother who is 90 and wants to have a page so she can also keep up with the family.
The kids are also friends with teachers, church people, work people, and neighbors.
Remind your daughter if she would not curse in front of an adult in person or speak about inappropriate subjects face to face with these people, she certainly should not say it in black and white on the computer where everybody will know all of her business.
We make specific rules about the use with our family since we can all see the wall posts, to remember people of all ages can see everything!
All people speak differently with their closest friends than they do their parents, just remind her to keep it in mind that she represents herself, but more importantly the entire family.
She will be in college soon and then you will have no control over how she represents herself. This is a good way to have a conversation about her reputation.