I agree it's her thing. Would you be as concerned if you calculated a friend's calories are they were grossly overrating? If so would you confront them? I'm guessing not. Eating is a personal thing. This is even a touchy subject with spouses or a parent/child relationship. As a friend I'd back off. People are much quicker to judge those who they believe are under eating, at least in my personal experience. There have been times I've been at a very low calorie level and any comments from others were unwelcome and irritating. No one said a word when I was gorging myself and gaining weight.
You intentions sound admirable but I'd keep it to yourself.