J., you are lucky that you live in a small town and that it's a small school. The law officials have time to take this seriously - in fact, they can actually talk to all these parents.
I realize you are worried about the cost to your daughter, but this is a learning experience for the entire school. Kids frequently ignore the real-life problems of allowing poor teachers in the classroom because they aren't mature enough to realize that a person who doesn't do their job, no matter how likeable they are, lowers standards across the board. These same kids, when they grow up, will want a teacher JUST LIKE THIS ONE to be fired because he or she isn't teaching their children. Preparation for college and a good job/career after school trumps a popular "coach" any day of the week.
The kids decided they needed a scapegoat because treating an adult like this would get them in trouble. What is very important is that the school treats this as more of an offense than if they had facebooked stuff about the superintendent.
Make sure that you don't mention to others about the reasons outside of poor teaching (you mentioned that in your other post, I think). You don't want people making stuff up as to what those other things might be, and it would come back to bite you in the butt.
Tell your daughter to hold her head high and get through the week. Within the month all this will have blown over. And tell her to remember her REAL friends. I'd invite them over in a month or so for pizza and movies.
I hope that you have an adult friend who can monitor facebook on her own daughter's site, because it very well may be that several of these kids block your daughter from their fb so that she can't see what they say about her. And THESE are the things you shoud monitor.
Hugs to your daughter.
Dawn