@Shane H. I'm surprised that as the master admin, you don't see a "delete" option next to the current accountant user. If all of the accountant user slots are in use, the "Invite" button will be grayed - but you should be able to delete one of the users. That piece would for sure be QB support question.
As for, ownership of the data, that actually lies with where it began. If this bookkeeper started your books for you, she owns the data. If the Quickbooks file is part of her license, she owns that, too. However, if you provided her access to your books, the data is yours.
This is from the Quickbooks support community, where a bookkeeper asked if they needed to give up the file to a client that hadn't paid them:
"If your client brings the QuickBooks file for you to start with, then you must return the original data to them.
If not, then it's your preference to give the data to your client or you must not give the data.
In addition, if you're referring to the QuickBooks software, it depends whose name the license is under."
That said, backing up what you have access to and starting over isn't the end of the world. Yes, it could be time consuming (not totally sure you have to restore the data to desktop and then move it back again - it's worth double checking), but at least you still have that access and it's not like you have zero books whatsoever. :-\ And then that way, you can set up this new/duplicated file on your own QBO subscription, which your new accountant can still wholesale bill for you to pass on those savings (I have clients set up this way - they own the file, but they get billed through me).
I hope you're able to come to a resolution on this soon! I'm so sorry you're experiencing this. There are definitely better ways to be spending your time.