That happened after she was fired. You can't cite that behaviour as a reason for firing her. Violates causality.

I went back and looked at Timnit's twitter history. She has a history of calling out her bosses and saying outrageous things, from well before this incident. People have linked, for example, a tweet where she called out Jeff Dean based on things he said in an internal meeting, and he had to do a bunch of apologizing and backtracking. I can't see how an employee can remain viable after doing that.

Her spat with the Facebook guy was before that.

That was a public argument on her core area of research. Google literally hired her to do that work. Being professionally assertive isn't toxic.