The movie was finished and shown at festivals in 2011, and was in general release during the the summer of 2012, it didn't get much play because the budget was tiny.
I agree, Gershon is hot, especially in the scenes where we first meet her, and the drumstick scene.
As to the ending -
Dottie is caught in her dysfunctional, possibly incestious family. She meets Joe, who she sees as a possible chance at a more semi-normal life for her and the kid. As the film goes on she sees Joe's darker side, fast fwd to the trailer scene -
Joe is beating the family, Dottie get a chance at the gun, she shoots at him trying to stop the madness. She shoots the father and brother by accident or by happy coincidence/subconciously. With her family out of the way, she's out of one dysfunctional relationship, now she's must decide if she goes with Joe. She realizes that she'll be jumping right back into the same sort of thing. Her finger wraps around the trigger.