^^^I think she can act. I just don't think she's been given very good material to work with.
So she faced no difficult decisions serving on a starship for seven years? No colonies being attacked, no situations where a sneak attack from an enemy may come?
She served with Georgiou for seven years and never came unglued in a situation? I don't think that vets of the Iraq or Vietnam war have to actually see those people to be triggered into having problems. PTSD doesn't work that way.
I'd say probably not. - IE no, they had probably not encountered a situation that escalated in the same way this one did in the past 7 years.
The fact it was Klingons didn't help, but I don't think the fact it was Klingons was something that 'triggered' anything. It was the whole situation:
- It was a setup (IE the relay was destroyed to bring a Strfleet ship here)
- After seeing the Klingon on the Beacon Burnham was tyerying to understand what the setup was
- After seeing 24 ships (and she knows the Klingons have 24 houses) she runs off the Bridge to consult with Sarek. (Because he's a Vulcan Ambassador she can tap who may have more info on klingon motivation as she knows Viulcan has had diplomatic relations with the Klingons before the Federation.)
- Once she consults with Sarek, she has (in her mind) a clear idea of why the Klingons have set this up and relates that to Captain Georgiou; INCLUDING an action Burnham believes will ultimately end the situation and save everyone on the ship. She further believes that if they DON'T take said action, everyone on the ship will die from a klingon attack - and a war VS a unified klingon Empire could be the result.
It isn't PTSD that drives Burnham to mutiny once Captain Georgiou decides against the Vulcan Hello; it's Burnham's internal (and to her logical although it's driven by her 100% emotional connection to her Captain and crew) decision that the Vulcan Hello is the ONLY thing that will save the ship.
It also isn't PTSD that drives her heat of the moment decision to kill T'Kuvma. If a Andorian/Tellerite/<insert favorite alien species here> had killed Captain Georgiou under similar circumstances - Burnham would have done the same thing.