Firstly, inform your line manager. Secondly, let her know that it is school policy that teachers cannot have anyone connected to their jobs on facebook accounts if they have one, and that the school does not even want teachers to have facebook accounts. This is true of many schools anyway. It's safer for teachers to not have facebook accounts to school management, it saves potential problems. If she finds your account on facebook and requests becoming a friend on your account, just ignore it; but inform your line manager. You may want to ignore your facebook account for a few months. Best of luck.