how do you know someone had already been shot?
I don't.
That is why I gave both options. IF she had already shot someone, then the call ought to have said 'she's shot someone'
If she had NOT shot someone, yet was going berserk, why did June, and the twins not wake up?
Furthermore, with either option, her 'berserk' behaviour was not particularly random, she shot each at close range, in what could only be described as a fairly controlled and logical manner, whilst not shooting at any other object - which is at odds with 'berserk'