It is amazing how many points of failure there were here, all of which could have been an opportunity for the woman to do something to better her life.
Obviously, she should have been armed and prepared to defended herself from home invaders, especially slow noisy home invaders who took enough time to break in that she could chat on the phone with 911 about the situation.
However, this wasn't some random guy... it was a "boyfriend" who was giving her trouble for some time already. Nowhere during this time did it occur to her "Gee, I could be in danger, let me go do something about that. Maybe I can ask a friend to teach me about guns."
And, go back in time further, and you'll get to the time when she first decided that this shitbag should become a "boyfriend". Really girl, you need some discernment in your life! What kind of an idiot meets a violent loser drunk tweaker criminal shitbag and thinks "Yeah, I want him in my life". You did it!! And no, I doubt he was initially all gentlemanly, dressed in a suit, bringing flowers and holding car doors open for her, then all of a sudden went bad. It just doesn't happen like that.
And nowhere did I mention police being a failure. Police have their uses, but in this situation their only use should have been to bag the body and file a report.