The obvious - has she started any medications (e.g. contraceptive hormones, any other medications etc)? Though her GP should have noticed these. She's also getting to the mid life area and most women will tell you your body shape does change as you age. Maybe have a chat to her mum and grandmother or older sisters if that's possible and see if this is a genetic pattern for the family.
It sounds like she's eating a fairly restricted diet, but made up of a fair amount of carbs (though good carbs). Perhaps try changing the fruit/mueslibar at lunch for a tuna or lean chicken salad or salad sandwich with wholemeal/grain bread (less sugars via fructose and the grainer the bread the lower GI and more fibre). Also it's worth considering that too low a food intake has been known to slow your metabolism. Also look for hidden calories and liquid calories - she may have restricted her food intake, but is she drinking 5 full cream coffees per day, or downing a few bottles of sports drink or juice per day?
They say 30min of exercise per day to maintain cardiovascular health - you would need to do more than that to lose weight though (but I'm guessing from her degree she would know that?), perhaps she could up that? Increasing cardio will help burn the weight, increasing resistance training will build muscle to increase basal metabolic rate. If she does the same thing every time she's at the gym, it might help to change things up a bit.
If she's studying she may be stressed - stress will mess with all kinds of things and has been known to influence weight. Find some way of de-stressing (meditation, relaxation exercises, exercise!). Also sleep levels - make sure she's getting her 8 hours since sleep problems have been linked to weight gain. Studying generally also means a lot of sitting around listening to lectures and reading - I don't know if that's the case for dip sports, but if so, that's a lot of sitting around and she might need to offset that with some more exercise.
Get her to keep on at her doctor because it sounds like (unless she's seriously kidding herself and is secretly eating a kilo of chocolate per day) that there might be something unexplained going on. Get her to start a food and exercise diary so she knows EXACTLY what she's dealing with. She can work out how many cals are going in compared to going out which will give her an idea about whether she's just miscalculated or if there's really something wrong. A GOOD doctor for this kind of problem will want to see one of these anyway.
It sounds like she invests a lot of her self worth in her body image, try to be encouraging and let her know you love her just the way she is and she's still the same person. She's likely to be a bit sensitive so try not to make disparaging remarks, even if they're well intentioned. The good news is if she's eating and exercising she should be relatively healthy cardio vascular wise even if there's a bit of weight creep.
35kg lost. (November 2005 - October 2006)
15kg gained again (as at October 2010).
Back to the drawing board - Let's do this thing!
"You can't change the winds, but you can change the sails"
"Reach out and take control of what lands in your lap"