Saddles are not just universally comfortable or uncomfortable -- otherwise, the uncomfortable ones would exit the market and we'd be left with only the comfortable ones.

There are many ways that a saddle can cause discomfort and the OP will have to get more detail from the GF before he (or any of us) can solve the problem:

A comfortable saddle is wide enough in the rear to support both of the sitbones, but is narrow enough everywhere else to prevent chafing the inner thighs. A saddle that is rounded on top works for aggressive riding, but may not otherwise. A saddle that is adjusted with the nose too far up may cause unwanted interference with the genital region when leaned forward. Similarly, a saddle with the nose adjusted down too far can cause the rider to slide forward on the saddle, putting too much weight on the hands and again causing discomfort in the rear because the rider is now sitting on the narrow nose of the saddle. A saddle that's too high can cause chafing because the rider has to slide back and forth across the saddle to work the pedals. Saddles that are squishy to the touch seem like they would be more comfortable, but once the full weight of the rider has caused the sitbones to sink to the bottom of the padding, the central part of the saddle again presses uncomfortably on the area in between the sitbones unless it has a well-executed cutout down the center.

So there is saddle width, top shape, adjustment, hardness, and probably other factors that I'm forgetting.