hi medhismummy, Ive had a read through. I'm sorry you've been having such a rough time recently.
There are lots of facts in your favour
-There is a new cash control policy, which you haven't been trained in
-You are under a lot of personal stress, have asked for support and not received it
-It has been made clear to you that time off will not be looked upon favourably
-When this came out, if I've read it correctly, you were not suspended and were actually allowed to work in charge of the safe again. It will be very difficult for them to claim that all trust has gone and therefore you must be dismissed. If they didn't trust you or if there was any doubt, they should have suspended you.
-Others have also been in the safe when they shouldn't have.
However,
-When you first found out the £20 was missing and checked your pockets, and found it, you didn't own up straightaway, instead you went into the safe when you were not on shift and put it back. I don't think lack of training in a new cash control policy will get you out of that one.
-Others also breaking the procedure, does the relevant person know about it, and has it been addressed? Will bringing that up involved 'grassing up' others including your manager? That will impact on your working relationships.
-You say yourself there are too many managers and they need to address that, you feel this may be an excuse to do so. That's key for me.
The first thing I thought when I read that you were convinced they knew it was an honest mistake was 'What else is there then? If they fully supported and trusted this person and valued her as an employee and wanted to keep her, and believed it was an honest mistake, they would do so.' Then you said about the stress you'd been under which has no doubt affected your performance at work generally, plus the too many managers scenario, and it becomes a little clearer.
IME there is always, always more to it. Rarely is there a completely isolated issue with someone. If there is a disciplinary issue there is often a work performance issue, an absence issue, or something else, which colours the situation. Same here. Some context which gives a clue as to their motives and the things influencing their decision making will help you decide how to address it from your point of view. It's never black and white so understanding their motives and being able to work out what you think their end goal is is key.
I think it's clear that their end goal, if long-term, is to get rid of you. That's my interpretation based on everything you've said. They may not be able to do it with this, given all the mitigating information you have, but I maintain the belief that that is the long term aim. Important for you now is to make sure all the mitigating information is conveyed clearly, is on the record, and try to get the fact that they do believe it was an honest mistake on the record as well. Write down everything that's happened so far so it's clear in your mind.
Have they put down in your letter exactly what the disciplinary is about? I think you need to put in a document yourself, laying out all the mitigating factors, so that it's all down on paper before the disciplinary hearing. Send it to them beforehand. That way you are not scrabbling to remember everything in the meeting, getting confused and flustered and relying on someone taking notes to make sure it's all on the record. Take positive action and put all this stuff on the record yourself.
Have a read of this from Acas about the statutory disciplinary procedure. Also read your own disciplinary policy. Make sure it is being followed to the letter by them - any breach of either their own procedure or the statutory minimum procedure will be helpful to you later, if you appeal it or if it goes further.
You need to think about your health and also your working situation. Do you think you can continue working there after this? I understand that there is more riding on this job than just a job, so that's a big decision, you may feel as though you have no choice and must stay at least for the time being. In which case you need to work out long term how to make that more bearable. If you make clear in your disciplinary that you are keen to improve your performance and contribute but feel that you need a bit of support in the short term, hopefully you should get that. If you make it clear that your doctor wanted to sign you off with stress but you felt under pressure to come in, hopefully you will be able to do that, and hopefully you will get the additional training you need as well.
If they dismiss you I don't think that could be considered fair, bearing in mind all the mitigating factors I've mentioned, in which case you'll need to appeal the decision and may hvae to take it further. I would suggest for the moment you focus only on the disciplinary hearing, and not panic about what other action you might need to take for the time being. Take it one step at a time.
Write the document I've suggested, putting your case forward and making clear all the factors in your favour you've mentioned. Make sure you take someone with you to the disciplinary, plus copies of your document, so you have it in front of you to help you. Keep your own notes of everything that happens, that way if it does go further, it will be a lot easier.
I hope that helps at least for the time being, do come back as well if you need to.