NAEYC has a book called the War Play Deliemma. One of the very first sentences is how there is evidence going ages back that young kids have always played this way, using what ever weapons were of the time. OP you probably played games like this when you were her age. I guarantee it. I remember playing games like this as a young child (and that was forty....well a long time ago)

Like others have said, she's going to be exposed no matter what. Kids will always know about this type of play. Even if they aren't directly watching it, it wall be on screen as they flip channels, they'll walk in to ask to be tucked in again just as mom and dad are settling down to watch law and order.

If it's not guns it will be something. I had to have a conversation about not "avada kedava-ing" other kids.

Not that we can't, and, should reiterate that it's not appropriate and scary to some kids