While we wait for more information, I like to comment that legal and psychological folks have argued about two things:
1. Given a history of abuse, can an action taking without a clear attack at the time be justified as some kind of pre-emptive or preventive action and seen as self-defense. The answer to that is strongly a NO.
2. Can a history of abuse be claimed to have produced spousal or battered wife syndrome for an argument of some kind of mental illness, diminished capacity as to excuse or mitigate the actions. That is very shaky in the mainstream psychiatric/psychology literature and in the scholarly legal literature. It is brought up at times, however.
We should wait for more information before speculation on these topics.