Sorry to be pedantic about a hypothetical, but I think it's necessary to consider the specifics of the actual case. Assuming this process involves something akin to a codebase commit, where the contents of the approved change can be clearly seen by the approvers, it raises the question of what sanctions her colleagues faced if Spiers' violation was so severe as to result in near immediate termination.
(because obviously, in your hypothetical situation, your supervisor would be fired if they knowingly approved a deceptive work expense)
If the supervisor did not know, then your analogy is flawed. There was no information asymmetry between Spiers and her reviewers - they knew what the change did and they approved it.
So in this case process was followed, yeah. But trust was broken, and it only stands to reason that Google would fire this employee because of it. All other stuff is secondary and pollutes the discussion.
How do you think old-school labor organizing went down? Do you think the bosses stood there smiling as employees handed out flyers at lunch? Google shouldn't have a say in how employees unionize. They have every reason, literally EVERY SINGLE REASON to sabotage it at every stage to make it as ineffective as possible.
In my company, I could put in travel orders to let me go to and from Hawaii on the company dime, have a vacation, and have my supervisor approve (which is following the standard process), but doing that should get me in a lot of trouble and/or fired.