I like the idea of giving her limited access. Something like one HD gun and a enough ammo for a realistic scenario.

My worry comes from the angle of the kid's friends and how much you trust the people they might bring into the house. The real catch 22 is that when the kid is home alone is when they might need it but also a time when there might be some mischief about that could lead to another kind of real danger.

Obviously case-by-case, kid-by-kid and all that but it's something to consider.