While there are probably a few uses of FB that are kosher and possibly even positive, it is a makom sakanah. One should question whether such social networks are really a need or just another piece of entertainment.
I figure that Bais Rivka felt it was a need at one point (for the sheer dollar value they hoped to obtain), and came to realize the price of how it endangered the girls was not worth it. From the reports I read, the school retracted its advice to join FB, and then had the students commit to delete their accounts. They only reacted punitively when several girls who committed to delete their accounts did not keep their word.
Far more important is that this FB issue is being turned into a discussion of whether the ban is proper, and how to deal with compliance – discipline. I think this approach is mistaken. This issue is an opportunity to teach something. And every such opportunity missed is a chinuch failure. If Bais Rivka did use it to teach, kol hakavod. If they or others do not, I feel bad for the damage they leave behind.