Have a plan for the shift. Let everyone else know what is expected of them. Ask for suggestions re some situations, but if anything gets out of hand, take charge and let others know some situations are non-negotiable, ie: that you are the boss, not them. Always respect the patients, carers and other nurses and follow the law. Discipline staff members in private and try to double-check work is done. Always make yourself available to other staff, patients and their families for help or questions.
There is a lot to know as a charge nurse. Some people don't know how to manage things - can this CN go on a course? Or just complain about her. I certainly don't tolerate crap now, and neither should you.