First thank your dad for his service and for standing ground on arresting that stupid boyfriend. Violence against any person is unacceptable, even worse domestic violence.
Unfortunately her behavior is not uncommon. There is something deep down messed up in people like her for clinging to an abusive boyfriend. It is a little bit like alcoholism, unfortunately they need to see for themselves that they live in an abusive and toxic relationship and she will need some serious help figuring this out and getting ready to leave. Look at the argument she used: He cannot miss work. He made her totally dependent on him. From what I have seen, his behavior will not change. It will only get worse. Maybe this is a necessary wakeup call...
From my own experience: I have been in one abusive relationship (mostly verbaly / emotional) and every time I was treated like crap, I loved that women even more and did everything I could to make up for my failures (I did not fail her, she just enjoyed making me feel like crap, especially when she was drunk). She finally ditched me over some stupid misunderstanding and that may have saved me. But not after some hard trying to get back together. Finally realized what had happened and that she was just emotionally abusing me. That was the day I could finally close that chapter of my life and feel sorry for her (almost at least, I still think about her every now and then). I cannot explain why I did go through all this. She made me so miserable day after day and was totally controlling. I just cannot explain it. Today I know I should have seen the warring signs all along. Alcohol on her part may have been a big factor.
So I know what it feels like and how hard it is to see the truth.
P.S. I just re-read my post and will not change it, but I did realize: I defend her ditching me... excused it by a misunderstanding. Crazy, even so many years later she still has mind opens over me...