Thank you for your question.
What follows may not be what you want to read. However, please do not shoot the messenger. While I can control the quality of an answer, my control over the the content of an answer is restrained by the truth.
A successful defamation plaintiff must typically show that:
1. The defendant made a statement of fact to a third party regarding the plaintiff;
2. The statement was not true;
3. The statement harmed the plaintiff.
The problem with the situation you describe is that you did grab and pull her arm. Further, the phrase "caused a riot" could be interpreted in many ways (for instance, "made a scene"). Therefore, whether or not the statements were actually false could be called into question. Regardless, it sounds like the statements may have been based in truth, even if she should have let the matter go. Unfortunately, a person can repeat things that would better be laid to rest, provided the statements are true.
Further, its worth pointing out that by touching her in a manner that would be unwelcome and offensive to the reasonable person (by grabbing her arm), you may have assaulted her. Therefore, she could turn around and file suit for assault, assuming the elements are met.
You mentioned that the deputy director is vindictive. While an employer may typically penalize an employee for such actions, if you believe the employer only did so due to prohibited discriminatory reasons (age (over 40), race, sex, religion, national origin, disability, pregnancy), that may serve as grounds for a lawsuit. The fact that witnesses and the union might testify favorably may also support such a matter. You will want to discuss this possibility with your attorney and, if you and your attorney feel that discrimination may have been the reason for the disciplinary action, you may decide to file a complaint with the EEOC. However, the nature of the actions you took may still hurt your case. Your attorney can help you evaluate that as well.
Regardless, many attorneys offer free consultations for matters like defamation. You may wish to consult, in person, a local attorney to get a thorough evaluation of the matter to determine whether or not pursuing a case would be prudent given the overall details of the circumstances. Your local attorney can help you make such an evaluation.
If you need additional clarification, please ask a follow-up question and I will be happy to elaborate.
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