If you love her, have her move in, file a restraing order / no contact, and get firearm training if you haven't already. Oh yeah, concealed weapons permit and a revolver ( very dependable)
However, I would suggest you think this thing through thoroughly before you make any decisions, cause your life is gonna change in a big way.
Don't be suprised if she begs you to smack her around when you have your first fight .
If you don't love her, but want to help her, you're still gonna need to protect yourself from the P.O.S. boyfriend. Think hard.