Probably a bit naive?
Security tools, and especially extensions that run with full browser access, are in an exceptionally trusted position. Employees who can inject code into arbitrary websites can in effect get administrator access to anything in the company, as Google is run almost entirely off of web apps of various kinds. It's actually hard to get more trusted than that: without a doubt this woman effectively had a greater level of access than Sundar Pichai or other senior executives.
If there's one thing you don't screw around with in any firm, its mis-using administrator access. Mis-use here means doing things that aren't related to your job description. You just don't do it! What she did would be like a logs engineer deleting internal access logs to cover up activity by political allies, or a GMail engineer spying on conversations between executives. It's complete madness to think you can abuse such a high level of trust in such a direct way and get away with it!
I used to have a certain type of Google account system administrator access. The way I used it was watched very closely, and deservedly so. Eventually it was removed because Google built better security systems that could restrict employee access more, and in my team were happy about this (for one, it meant we were less likely to be hacking targets). The idea of anyone abusing this sort of access for political reasons was unthinkable.
I honestly can't believe people here are defending this kind of behaviour. If Googlers feel it's OK to abuse root@chrome for unionisation related purposes, what else might they start doing? What about people perceived as 'bad'? Google needs to explain what happened here pronto, because apparently she was able to get this change through code review? So she had internal allies who approved her abuse of access? That is tremendously worrying.
Google is very rapidly burning the trust it requires for its business models to function. How can anyone trust the firm when 21 year old activists are able to manipulate Chrome for political causes and Google's own security procedures are unable to stop them?