Halloween has always been part social catharsis. People dress up as things that scare us, or ‘offend’ us.
This costume is at least a couple of years before it’s time (the wounds are still open); but, it’s certainly not over-the-top, as costumes go.
(I left my asbestos suit at the cleaners, so please don’t flame me. I’m just providing a little perspective.)
If she had dressed up as Dzokhar Tsarnaev, with tire tracks across his head, she would probably still be employed.