It looks like your girlfriend has long arms and legs and a relatively shorter torso. For a WSD bike, it depends on how much that short torso affects her functional reach. Often, people with a shorter torso can ride a bike based on their inseam length because those with longer torsos sometimes have a harder time closing their hip angle (bending towards the bars) enough to reach well at that length of the top tube. Though a long femur length could mean pushing the saddle back farther, thus making a shorter top tube or stem more desirable.

To me, she looks too big for that 57cm, but it's hard to tell from a picture.

I guess everyone's point is that we're all quite different. I am only 5'7", have a 32-33" inseam, and am fairly long backed (not long waisted), but I ride a "men's" 54cm. I could go down to a 52cm on some Treks. I tried a WSD bike and felt unbelievably cramped, though my hands liked the smaller bars. That's something you can easily swap out on a larger bike.

I'd be inclined to say that at her height, she needs a bigger bike, and probably a men's bike. Maybe some adjustments like narrower bars or shorter stem are in order to get the best fit. But really the best thing to do is to have her get on a bunch of them and ride around.