I think you can only control what you can control, and the rest of it, we leave to life to figure out.
No place in the world is ever going to be 100% safe. Nowhere. But I also strongly believe that we shouldn't stop living because of our fears. We take calculated, educated risks and do our best to prevent the accidents we CAN prevent: have our kids wear helmets, wear their seatbelts, we don't use our phones while driving, we wash our food before eating it, we make safety plans with our kids should they get lost, teach them the difference between medicines and candy-- these are the most immediate threats to their safety, NOT teen shooters at school.
We live in a very uncertain world, K.. I tell you, I live on a fault line and the media is always touting headlines that The Big One will come sooner or later. While it helps to be prepared, let me also say that I would go nuts if I let these fears eat away at my waking hours. So, we do what we can, have safety plans in place, and then we let it go and try to enjoy ourselves. That's what I would encourage you to do. It's also okay, if you are feeling constantly anxious, to talk to your doctor and get some help. It may be that you need a break from those chemicals being at play in your body. It can make us nuts, and we also need to take care not to let those thoughts take too much from us.
It's too bad your sister couldn't keep her comments to herself, but just because she said them doesn't make where you live any more dangerous. It's just her perception. It doesn't have to be yours.