Why would she do that? Am I being paranoid?

My boss gave me an outstanding review report and then started to bash me. She's trying to blame me for her mistakes and is misconstruing events in a subsequent report she wrote about me. I have a right to write a rebuttal to the report (per union contract) during work hours. She is very defensive of me using work time on the rebuttal and said I called in fake sick so that I can work on the rebuttal even though I had submitted a doctor's note per her request. Why is she against me working on the rebuttal? I have completed all my assigned tasks including writing procedures for my work tasks.