LW, RUN AWAY. Animal abuse is a terrifying precedent, she should absolutely never be left alone with a child.

(I have raised a child to adulthood, I can't handle a dog, and I am OKAY WITH THAT, which is why the girlfriend should have taken him up on the offer to board the dog with a qualified dogsitting service. Even if she'd been overly optimistic and got in over her head, THAT OPTION WAS STILL ON THE TABLE, she could have dropped off the dog rather than abused it.)