She gave her employer an ultimatum, threatening to quit if she didn't get her way. They called her bluff. I don't see how that is the same as being fired. At that point she was on her way out, one way or another; most employers would rather not work with people like this.
"Do these things or I'm gone and taking my team with me"
and
"These things are so fundamental to my role as an ethical AI researcher that it's difficult to see myself doing this job without them"
IANAL, but I suspect a court would also interpret them differently.
And even so, Google likes to position itself as a nice employer, which listens to their employees' concerns. De-escalating the situation would have been nice - immediately terminating the concerned employee makes Google seem like another giant faceless emotionless multinational corporation (which it may well be).