Preacher
Well, probably she was just pissed off at him for something and shot him in the middle of an argument. She probably is psychologically unstable and handled the situation in the wrong way.
As far as what to use as a defense. If I was an attorney, I would probably choose to use child abuse, as it is an emotional issue, and could do more to garner sympathy for her. This is used quite a bit now by the woman in custody disputes, etc.
Unless she gave some other motive to police, then will have to come up with another, such as insanity plea, etc. They could use the "God or the devil made me do it, in that case.
Interesting that if he would have killed her, they would be talking more about how to execute him. But in this case, they just keep asking, what he did to make her do it. But that's the way it always is.