I don't know why there is this pervasive desire to strangle developers. This is a pretty recent phenomena in my opinion and certainly nothing close to a requirement to develop great software.
If I were an employee at Google, actions such as this would let me seriously consider to look for other work. The requirement for the code review for internal tools already seems awefully restrictive.
Give employees power / freedom and fire fast if you do stupid things.
Stricter regulations/ checks so they cannot mess up hard in the first place. At the cost of slower pace and less risks taken.
Google has historically been the former. And it comes with people doing stupid things and getting fired. Just the world is not used for huge companies to keep operating in such mode.
I applaud Google for keeping being open and not enforcing processes. The rest of the world will grow up eventually.
But I fail to see how the employee in question did something that justifies firing her. Maybe there are other factors involved, but I certainly think that people opting for getting rid of her only on the basis of publicly available information shouldn't have any form of responsibility for staff to be honest.
How on earth is that restrictive? Having code review for any important code should be normal at any company. Just because the tool is internal doesn't mean it's trivial and any engineer (especially a 21-year-old: how is she even an employee and not an intern at that age?) should be able to merge anything in willy-nilly.
So to answer your inane question, she wouldn't be an employee because she's not old enough to have graduated college yet. And that's just to get a BS degree; lots of engineers these days (esp. at top-tier companies like Google) get an MS degree before they enter the workforce full-time.
I'm rather appalled that I have to spell this out here on this forum.