Pku in college was awesome. Where I went to school it was easy. I spoke with the head of dining services and as long as I had a meal plan they purchased all of my low protein foods and also would supply me with foods to eat in my dorm room. Not all dining services are going to be understanding but I am a commited dieter. I have never been off diet, will never eat meat, and refuse to ever even think about doing so. I am on 5 grams of protein. I was never tempted to eat anything not on the vegetarian line at school so it was a lot easier for me than it will be for your girlfriend. Having access to so much food at the same time can be tempting.
Your girlfriend is hurting herself if she does not stick to the diet, and it will be harder if she gets pregnant. A woman who is pregnant and not committed to the deit runs serious risks to the baby, including tremors, epilepsy, and mental retardation. This is because when the protein we (PKUers) eat goes into our bloodstream it essentially acts like an acid, this then transfers into the baby through the umbilical cord essentially poisoning the child.
I would say do all in your power to get her on that diet. She'll thank you in the end.