Girlfriend fitness dilemma

My girlfriend and I are both second years in college. She wants to lose weight and get down to or closer to the weight she was her senior year of high school.

She's 5'8 and I think around 135-140 but I'm not entirely sure about her exact numbers. I have absolutely no idea how she doesn't lose weight. She is on a super strict diet of ~1400 calories and follows it more strictly than anyone I know, counting everything with an iphone app. She's a nutrition major and cares a lot about diet and has tried various macro compositions. She's also our cross country team and runs more than 60 miles every week in addition to weights and biking/other froms of cardio. Her workouts burn minimum of ~600+ calories a day.

And yet she stays the same weight. Does anyone have any idea of what it could be because after reading r/fit and r/nutrition and following many blogs and making nutrition and fitness a passion of mine in addition to taking classes for it at school, i have absolutely no idea how this could be happening.

EDIT: thank you all for your suggestions, I guess I'll just have to wait and see. If it turns out to be something specific that is wrong beyond the usual diet failure reasons I'll make another post about it