It's also possible that she startled the dog. Not saying aggression is okay, but every dog has a threshhold to which various factors-- environmental, health, mental -- contribute. If it was a dark room, the dog was asleep, was startled, maybe heard a dog down the street bark, etc... it all adds up.
Which is my long way of seconding Alikins -- your girlfriend needs to actively become the dominant dog in their relationship.
In addition to walking her and feeding by hand, she can participate in training sessions. And you guys should be expressing your dominance in subtle ways, too -- get her food out, set it on the counter, and then proceed to eat your own food. Halfway through, give the dog her food (make her do a sit-stay for it). Ten minutes later, take away anything uneaten.
Become the controller of all resources -- toys, food, water, etc. Watch your eye contact with the dog and resist the temptation to watch every move your puppy makes, even though everything she does is cute and look-worthy.
In a dog pack, the followers will look at the leaders in order to follow their cues. If your pup often catches you watching her, she will assume you're waiting for her guidance.
Check into the NiLiF program and implement it... good luck!