Sorry it's been so rough, CopperStar.
One thing at least -- you are in a strong position regarding the cash drawers. You were wise to bring it to corporate's attention. And, most fortunately,
before the $80 incident(!) Both corporate and the manager are aware and agree with you that it's a problem, hence the new rule. Which the assistant blew off. It's 100% on her, AND reinforces with both corporate and manager why it is a problem, and how significant a problem it can be. Frustrating, yes. But Right with a capital R is on your side.
Like BeyondtheRainbow, I wonder if the med adjustment effects thing is at play. Seems like it could be. You say you couldn't do the job on them. And, as you are feeling now, without them. But those aren't the only 2 options. Have you had a chance to check in with your provider to see if something else might work better?
I know what you mean about the going alright but for blips after reducing (or eliminating) a med, only to realize after awhile that maybe it's not actually going so well. (Kind of there right now, actually.) No worries. So many of us have been there, which means we've had the "sunshine" days/weeks that precede it. You can talk about those too.

And because you're sensitive to *how* that might come off badly, it wouldn't. Because knowing it, you wouldn't write it that way.
One other thought. Maybe revisit the part time issue. After all, that
is how they presented the job when they hired you...