My perspective on this is different. For one, what the admiral did was prima facie evidence of entrapment. She's a trained psychiatrist, she sleeps with her patient, and then, rather than empathise with him, she blows the lid, accuses him of being broken, goes ballistic, and doesn't even follow-through on her threat right there and then. If you believe your patient is a threat to him/herself, you have an ethical--and, in some States, legal--obligation to report. She left him in command pending a formal complaint to--what?--Starfleet command? Chief of Starfleet Medical? Not sure. In any case, her actions, at least in my estimation, clearly indicated she came there under false pretenses and she found what she was looking for, however thin a fig leaf it was. That's horribly unethical, at the very least.
And what did she find? That Lorca has scars. That he sleeps with a phaser. That he reacts negatively when someone touches him--without his permission, mind you!--in bed, whilst he's asleep. That's hyperarousal, yes, and one of the symptoms we look for in PTSD. But it's not like she did a full evaluation right there and then. It takes more than a knee-jerk response to give a proper diagnosis. Also, PTSD symptoms do not present themselves immediately. They take time. And, more to the point, I'm not seeing him with a full complexus. He's demonstrated only two items, only one of which is a symptom: he's had a stressor--obviously--and he's shown hyperarousal. But, since it's only been one week--if you believe Cornwell--since Lorca's gotten the conn back, he hasn't shown the requisite amount of time needed to diagnose PTSD, which requires (as of DSM-5) more than a month of symptoms that--and this is key--have a negative effect on his performance or subjective experience. If it's less than a month--and, again, it has to have a negative effect on his performance or his subjective experience--than it's what we call an acute stress disorder.
In other words, she had no call to do what she did because he has not demonstrated marked deterioration in behavior, hasn't admitted to marked subjective experience, and, basically, seems like he's coping with it rather well, thus far. He's more resilient than others, mentally.
No, to me it looks like she came there to prove something, found what she wanted and, perhaps to cover her embarrassment at the awkward position she was in--at the wrong end of a phaser after she did a big no-no and touched someone in their sleep whom she suspected may have had an issue with stress--she quickly came up with her threat.
But, mind you, she didn't execute it. Why? She knew she had nothing to stand on. She'd read his evals and even if he admitted to fudging them--and, really, trust me, no one goes into that kind of test wanting to be COMPLETELY honest about it because they know what's on the line and even the psychometrists administering them know to take that into account--it's still privileged information. So...she never let the boom fall. She didn't immediately relieve him of command--which she could have done--but instead delivered a hollow threat. Until he's given a proper evaluation by an uninterested party--not someone you have a history with and with whom you've slept with!--his situation is actually pretty safe.
I suspect Lorca probably knows this. Hence his willingness to do things a man who felt threatened wouldn't do. Like reinstate Michael. On further reflection, though, he knows he walked too close to the line and, in the end, pulls back. Better to make sure his actions are impeccable than prove Cornwell's point.
