always think about consequences of calling the police
While we digest that little morsel do me a favor and think about the consequences of not calling them please!
I don't see how the OP's situation relates to domestic violence. I see girl alone at home no working knowledge of weapons. Call the cops period end of story. Anything to the contrary is a foolish assertion.
Someone made the argument of secure yourself first and then call the police. I can agree with that given that the person involved has firearms training. If not then 911 while moving to a secure location should be priority #1. The line may be cut by the BG so if you can dial do it now. Cordless phone or cell phone is also handy. ALWAYS HAVE A CORDED PHONE IN YOUR SAFEST ROOM THAT DOES NOT RELY ON ELECTRICITY!!!!
The DV stuff doesn't really seem realevant here.