sodapop, I don't read anyone here suggesting the killing was a heroic act. Heroism would have been to leave. These days she could report him to the police for coercive control, though victims of domestic abuse don't always receive the response needed.
Anniebach, many people who subject their partner to domestic abuse in any of its forms have one thing in common. They lack empathy, the have a need to control, they manipulate, exploit and alternately humiliate or charm their victim. That may constitute a personality disorder and leads to the usual discussion about personality problems and mental health problems. My view is that m.h. problems include anxiety, depression, psychopathy, schizophrenia for example. I'm on the fence about personality disorders which don't respond to medication in the way m.h. problems are likely to do. People can change their personality types - if they recognise they're damaging those they love, damaging their own life and truly want to. It isn't easy though.