Youch! Those words coming from Mom can really hurt. But even if Mom hadn't said anything, your girlfriend has reached the age where she must face the same truth we all face. There comes a point in everyone's (ok 99% of everyone's) life where you have to work for a fit body. We reach that time at different ages, and some of us must work harder than others, but there's really no way around it. The carefree days of our youth, eating whatever we want w/o any consequences, are gone for good.
Quick fixes last about as long as they take. Healthy eating and exercise need to become part of her lifestyle. We brush our teeth because we don't want cavities. If we want a healthy fit body, we must take care of it - we only get one! Results take time, but most of all they take consistency. A healthy diet need not be all doom and gloom, I still eat all my favorites like pizza and cookies, but since I eat healthy food, I crave less of the treat food.
Since she's at college in a new environment, this is a great time for her set some new good habits. The sooner she gets in the groove, the easier it'll be for her, plus she'll have a head start on all her friends who'll be trying (and failing) various crazy Hollywood diets, starvation diets, etc.