You're right, Cece... this could get sticky. My instinct says to do the following:
-Call mom (done)
-Notify administrator (first thing tomorrow)
If the administrator says she can stay on the squad:
-Have girl run after practice
-Put her on notice (perhaps even in writing) that the next time she posts anything of that calliber on a public forum, the consequences will be much worse, perhaps even dismissal (still thinking on that one, and will seek administrator advice)
I don't want to dismiss her just yet, because being on the squad has the potential to be a positive influence for her. But, I don't want to get to a point where she can do whatever she wants, make the squad look bad, and think it's okay.