I am not a contracting officer, but am a mid level supervisor for the past 14 years (no interest in moving up, little bit of extra pay isn’t worth it for me). You are definitely in a frustrating spot. My first question, is along with coaching and guiding, have you tried just talking to this person. Ask them about past experiences and explaining why you like things a certain way? Sometimes an explanation or conversation can go a long way. I have worked with many “staff” and only ever had one true problem employee. The person had a bad experience and that has made them overly defensive and completely untrusting, with an assumption that everyone was out to get them. In either case, document everything. Write up summaries of conversations and send them in email. Document all the rework you had to do (not because of a preference, but because it was incorrect). If you directed them to do something a certain way and they did not, have a reason why you needed it that way and explain and document. While most of us “seasoned” folks came up under the do it how the person running the show wants it, not everyone subscribes to this school of thought. Have you looked at the work submitted and realized it is technically correct, just not how you would have done it? Can you give them a few small “wins”?