She had already tried to kill the cop. That’s good enough for me.
Conjecture. The facts are that she backed up, hit the police car, and tried to drive off. Saying that she tried to hit the cop has just as much fact as saying that she was simply trying to get her car in a position to make a run for it. There are not enough facts to prove either supposition.
No evidence that she tried to kill the cop.
If you or I shot her under those conditions we would be up for murder.