Hello, thank you for your question, my name is ***** ***** I can assist with this.
I am not sure that I can see you have done anything wrong here at all. You're allowed to have an opinion, it's part of being human and living in a democracy. I suppose how you might express that can be an issue, such as if you disclosed confidential information to third parties not authorised to receive it, but there is no suggestion of anything like that in your question.
The employer should be stating, in writing, what it is you are supposedly being investigated and, if appropriate, disciplined for. If this has not happened, then I wonder whther in fact you have been formally disciplined at all and this was more likely to have been a manager simply taking out a bad day on you - quite unfairly!
So, from what you have said, I cannot identify what you might have done wrong.
Thanks do I have any redress against her or should I let sleeping dogs lie