Does it matter? If she used Google resources in a manner not company-approved, and if labor law doesn't recognize using a resource like that as a protected communications channel, like they would a company break room announcement board, why should Google be subject to a neutrality test? I support unionization, but I don't see what legal ground she has to stand on here.
The firing might hold in court, but to be frank there is no way she would get fired over something like this if it was not related to unionization or other anti corporate messages. Google is typically very lenient on harmless offences like this which is why the firing is a surprise.
>Google is typically very lenient on harmless offences
I know somehow who got fired from Google for taking a half gallon on milk home, because it was late and he didn't feel like swinging by the grocery store.