I think you did a great job of identifying what probably led to this. Hopefully the two of you can get past it with time and patience!
As suggested, I'd perhaps get her into a smaller tub setup - even just a 12-quart Iris or Sterilite tub might be a good idea. Be sure she has access to snug hides that touch her sides and back. It's possible that you could maintain her in her current enclosure if you block the sides and back and provide her with lots of clutter and hides.
I'd stop handling her altogether until she's clearly settled. While I agree with El-Ziggy that hook training is often a good place to start, I have to say that in a case like this where a baby snake is simply terrified, I'm not sure I would start with hook training. My personal preference with snakes like this is to use a strategy called choice-based handling that allows the snake to gradually adjust to your presence on their own terms. It takes time, but in my experience so far with multiple snakes of various species, the results are more than worth it.
I learned choice-based handling from an animal behaviorist and trainer who specializes in working with snakes - pythons in particular but other snakes as well. I'll link a video below she did on first steps in choice-based handling.
https://www.youtube.com/watch?v=4ljt...el=LoriTorrini