Call your BON and explain the situation and get their feedback. Take that to your nurse manager. While a charge nurse is in the chain of command, they are the chain of command during that shift (at least where I work) and do not make administrative changes/declarations. Also, every job I have applied to has asked me if I would be willing to work OT if needed and I aid yes, if I do not, that could be considered falsification of information on a an app and subject to termination....did you make such an agreement?
Once all is said and done and worked out, I would then let said charge nurse know that if she ever threatened me or my job again without sufficient grounds, I would report her to the BON before she could even apologize. I would declare this with a personal witness and the nurse manager for the unit as well as the DON/CNO present. That way all would know that I am not one for bullying.