Could be a territory thing, if you are primarily the alpha in the home. My best recommendation is that your girlfriend start in active training with her. Rewarding good behavior, and starting to be stern & reinforce correction when she acts out towards her. She needs to understand that your girlfriend is also an alpha, start with having her correct her every time. I don't know who feeds her, but try letting your girlfriend feed her, she will see that "good" is coming from her, and she has to respect her... Let your girlfriend walk her, etc. (if she's not already) Reward good behavior with small treats. The worst thing she can do is act scared... she will sense that and continue the same attitude.