Oh, come on, too late?
This isn't some crazed, unstoppable zombie from a horror movie we're talking about, it's a 16 year old little girl. You're seriously trying to tell me you think she wouldn't stop what she's doing if she hears a gun go off at close range? And that pause would be more than enough time for the officer to then use a non-lethal take down.
Absolutely no one needed to die here.