Old high school teacher is spreading rumors about me. What should I do?

So my senior year history teacher is my little sisters study hall teacher... Me and that teacher did NOT get along, but I thought we ended the year on a good note. This was 4 years ago. My sister was in her study hall, and the teacher was asked by another student which student was the worst for her... To my... show more So my senior year history teacher is my little sisters study hall teacher... Me and that teacher did NOT get along, but I thought we ended the year on a good note. This was 4 years ago. My sister was in her study hall, and the teacher was asked by another student which student was the worst for her... To my sister's surprise, she said me. The teacher went on to say that I stole things from her desk, called her a "B*tch" in class, skipped her class, screamed at her, etc. All of that is not true!!! I never did any of those things! what should I do? go to the school board? What if she's spreading other rumors about me to other students that I don't know about? She doesn't know that I'm my sister's brother. This is giving me mad anxiety.
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