Sigh. Nellie, honestly. After listening to this whole posting history...I think you are guilty. Many little things, many details in your story, things you've brought up are worrying me, creating the wrong images in my mind. Don't forget, I have heard many stories about things like this. My radar is pretty good for what is said and not said.
If you can't even convince us who want very much to believe you that you're being falsely accused, and you want to show your innocence in a employer hearing, you need an attorney to do your talking for you. Don't ask me exactly why, but your last comment, the "well, sometimes my old supervisor told us it was all right to do this!" you threw in there was the worst possible thing you could've said to convince ME of your complete innocence, which I was struggling with while you went through "my son can prove he wasn't there because he....was somewhere else...no wait, they didn't give him a pass...no....because he didn't ever wear my slicker....no because he's....." This story isn't holding together. And all the obfuscation about how the supervisor is a political appointee, etc. I try to tell myself you're just venting here, but it would be wise to talk as little as possible and let someone else talk for you in the hearing. (And not your sister.)
Someone mentioned this hearing not being so important, the termination is already a done deal, and the union lawyer is the one who is supposed to be representing you....IF you are covered by the union contract which now we hear that it hasn't been signed? Do you have a union or not? If not, still ask for his help, and do not let your sister go there and try to tell him what to do.
All he really needs to do is say, "My client is not guilty of this offense." You don't get up and "confront your accusers" and do a lot of talking and citing legal information. Neither does your sister. She needs to stay far out of this. Who is it she is emailing?
If they want to terminate you... you know the drill. An at-will state, not a court of law, if they want to they can. It seems they want to. This hearing is just a formality. Don't allow it to also be a farce which confirms their wisdom in terminating you. Act like the consummate professional crossing guard falsely accused, not the neighborhood nut case. If they want to press charges against you for stealing the $24, you do what anyone charged with a crime does. GET AN ATTORNEY AND SHUT UP.
In unemployment hearings we would frequently have somebody who was a family member or friend (though not an attorney) of the viper variety who wanted to come in and talk for the client. It was generally not allowed, unless the client was in some way unable to represent themselves, such as not being able to speak the language or being illiterate or having speech/hearing difficulties. The last thing they're going to want is a room full of angry vocal relatives of yours waving employment laws at them.
And if they've already made up their minds to terminate you, they will not listen to any of these arguments or pronouncements, they'll eventually go right on and terminate you (railroad you) right out the door. You just need to go on record saying "I deny that I did what I was accused of. I did my job to the best of my ability and you have no reason to terminate me. " You don't need to add that your attorney will be in touch, but make that happen.
Where you will "get justice" if you get any is in the unemployment system first, and then you talk to an attorney about their depriving you of your pension, and your termination, and your treatment by the school system.