Anathema
Crotchety Olde Man
There are likely other circumstances as well. Possibly the gun had a hair trigger, or that she made the mistake of drawing it with a finger on the trigger. Could have been drunk at the time, who knows.
In other places I'd seen it suggested that thus occurred while she was attempting to adjust the bra/holster for a more comfortable fit which tells me she shouldn't have been wearing it to begin with