Well, I won't comment on only eating meats & vegetables, but I have GD & will second the recommendation for fat. I won't, however, second the peanut butter. If you're adding fat, really add fat - oil, cream cheese, butter, etc. If she's eating low fat this should help a lot. And the exercise. I found for me personally very SLOW exercise (like trawling the mall slooowly) helped best. If it is really aerobic it doesn't really help me.
Eating whole grain carbs will keep your BS up if you have GD.
Your friend may find that the psychotic eating is all for naught and she needs to go on medication anyways. Not saying its impossible to control solely through diet, but it sounds REALLY extreme for a pregnant woman to only eat meat & vegs. There are a lot of us here on insulin or other meds (I take glyburide) that are very happy with our choices and we'd be happy to give support (check the humongous GD thread).
ETA: ok, i commented on only eating meats & veg. oops!