You are indoctrinated to one way of diving that reduces legal exposure. You don't dare step out of that box.
Isn't the reduction of legal exposure accomplished by evaluating risk and taking steps to reduce risk of injury? I'm not sure why you would consider that to change the litmus of whether something is simply a personality clash versus, as you say, doing something stupid.
You said "she has done stupid things underwater." Are you asserting that doing something stupid underwater would or could be written off as a personality clash? That is what you seem to have said.
In my experience as a diver - not an instructor - if you do a stupid thing while out on a boat, the captain may frown at you or he may blow your hair back, depending on the captain and on how stupid it was. But, it's rare to be banned from a boat. But, if you go out on the same boat a lot and you do stupid things repeatedly, you really should expect to get banned. And that is not Stuart, the Instructor, saying that. That is Any Person With An Ounce Of Common Sense. Calling that "a personality clash" is nothing but rationalization intended to avoid taking personal responsibility for doing something stupid. That is saying "we had a personality clash" instead of saying "I did something stupid and got called out for it."
Note: *I* did not say she has done stupid stuff. You did.