That's why my range bag(s) - just free tool bags I got from Dewalt or Porter Cable - are nothing but dedicated range bags. They never go anywhere but the range outside the house. Guns NEVER go into any other bag. When I've gone to Florida, for example, I've gone to a range and shot while there. The range bag went along, all gun stuff in the range bag, and my suitcase with clothes etc, had NOTHING pertaining to guns in it, not even ammo or so much as a screwdriver.
A TSA gun encounter is the big booby prize, but guns and gun stuff appearing unexpectedly at the wrong place, wrong time can at the least make some people uncomfortable.
OP, I hope your niece and family come out of this as whole as possible.