And your supervisor knew of your intent to deceive the company when they made the approval? And if so, why would they make the approval unless they too wanted to be fired?

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 your supervisor knew that you were taking the trip to vacation, why would they approve it?

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.

No, to follow the analogy: The supervisor trusted that person to only put in requests that are actually work-related. Just because the process says "supervisor approves" doesn't mean that it absolves the subordinate of responsibility.

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.

So forming a union (which is absolutely legally protected) is like going on a vacation?