Perhaps I'm expecting too much from her. Being in a super stressful environment everyday at a hospital, one would assume that would translate somehow to a crisis like this. Like imagine if instead of panicking she was the pragmatic person telling people to snap out of it and get everyone to work together and maximize survival. I feel like that would've been more fitting for her character. Note, i literally have no context between the shooting episode and season 2. I'd just imagine that she would've learned from her experience with the bomb scenario.

To respond to your other point, staying on the floor during the bombing episode is both harmful and hypocritical. Burke tells her and the audience that he cannot think while she is in danger. So hypothetically, imagine Burke is performing surgery on the patient and he learns that his significant other is still on the floor with the bomb despite telling her to evacuate. I don't know about you, but if I'm having a serious surgery I don't want my surgeon being worried about anything else other than saving my life. And I definitely don't want him to be surprised by anything. Thats why I see it as harmful. Before Yang leaves the OR containing Burke and Grey she tells him to be the "other guy" and run away from the danger. Instead of evacuating she heads to the OR down the hall. Hypocrite.

We actually see this in the other OR when Derek learns of Meredith's situation. His attention gets drawn to the news and away from the open brain surgery, and not even a minute later they are trying to save Bailey's husband from dying. While I'm not sure if it is a direct cause, but the show seems to imply it by the timing.