A gun went off. She was responsible for that. Whether she really wanted to kill him - either pre-determined or right then and there - is another matter. No, you don't mess with guns in front of people. But she's not the first and she's not the last who might have had a blackout in a relationship strife.
Granted: That she called her attorney first and an ambulance only second is a disturbing detail. I'm not saying she isn't guilty of manslaughter or deadly assault or whatever, but as a lawyer I'm prepared to give her the benefit of (a little) doubt, you know how we are ...