They do. Which is why you never point a gun at someone, let alone pull the trigger. It’s an entirely implausible excuse because what she did has nothing to do with teaching gun safety.
It may or may not have been an acccident but it happened because she was bullying the child. Whether proving that level of intent is enough to prove murder (in the US), I don’t know. But at the very least it is an extremely serious form of manslaughter so the difference is probably negligible in terms of conviction and sentencing (unless they can prove that it was an entirely deliberate and intentional murder).