I am fairly certain that there's an idiomatic phrase for this, referring to either the situation or the person. It's on the tip of my tongue.
Scenario: Alice tells Bob to stop making a such a noise with his power tools. Bob replies that he had already stopped an hour ago and was anyway done for the day.
How would you describe Alice, who instructed Bob to do something which he already did or was going to do? In other words, she gave him a redundant order that serves no purpose other than to reaffirm authority and stroke her own ego. Alternatively, she's making a show of strength by demanding that something that's already been done, be done.
It's similar in concept to the French phrase "faire la mouche du coche" but not quite. It's along the lines of gadfly, backseat driver, busybody, or tooting one's own horn.
EDIT: The closest matches so far are control freak and megalomaniac, but those still don't describe the post-facto aspect.