That is probably the most common way to carry concealed, so I wouldn't really doubt that part of the story. But not much else makes sense, and there seem to be some conflicting statements. Did she approach him from behind, or from the front? The story says he didn't know her, so why was she even touching him at all, especially while he is dancing with his wife? Something don't smell just right.
This would explain a lot -- gun that killed Adaisha Miller had trigger that could be reached through holster
.. but then how does she manage to get shot through the chest?