kunilou, I was in much the same situation as your daughter when I was in high school - I was five feet even, with C-cup breasts by the time I was 13 years old, and to my horror they got bigger later - with the exception that my father was the ONLY one who would talk to me about it or who actually managed to make me feel even a little bit better.
It never bothered me that my father had these kinds of talks with me; for me, it would have been much worse if my mother had. (It would have embarrassed her, which would in turn have embarrassed me.) But YMMV. It sounds like most of the women here did not have that kind of relationship with their fathers, and also you have to be the kind of person who can talk about sex calmly and comfortably. (My father is notoriously matter-of-fact about stuff like this. The stories I could tell…)
But don’t think there’s a magic bullet. I know my father, at least, always wants to say the ‘magic words’ that will fix all our problems, but there aren’t any in this situation. Nothing but time is going to solve the problems your daughter has with her body. It’s hard to explain, but big breasts are like this giant mutant fungus sprouting from your chest that everyone feels free to comment on. They’re sort of ever-present, obvious symbols of all the changes that are so embarrassing and hard to handle, plus being big-breasted really does alter your life. Guys do make comments, stare, etc., and I don’t think they realize how mortifying it is to younger teens. (Example: when I was about 14, I went to the gym at our local military base with my dad and mom. I was hesitantly working out on some Nautilus machines, feeling very out of place, when two Marines in their early 20s walked up and, with much nudging and leering, asked “Need any help with your CHEST…exercises? No, looks like you’ve already been doin’ some good ones!” I got up and ran to the women’s locker room and refused to come out. A female officer who happened to be in there got the story out of me and then went for my parents and told them what had happened. I know those guys meant no harm, but at the time - it was just world-annihilating. I can’t explain it, but it was.)
So you can’t fix this. She’ll get over it eventually on her own (unless she has lots of other body image problems also); college, coming up, will be a big part of that. In the meantime, if you have that kind of relationship with your daughter, you can ask her frankly: “What is it that bothers you? Is it what men might say? Is it being noticed? Is it that you don’t like the way you look?” She might just tell you, and these problems can be solved, to a certain extent - there are other kinds of clothes that mask it (though I am STILL partial to the potato-sack look), as people have mentioned. Self-defense classes can help build confidence and reduce fear, not to mention improving her posture, which has almost certainly suffered (there’s an instinctive hunching thing most women do when they feel self-conscious, and believe me, walking around like that 24/7 for years will screw up your posture and your shoulders).
Beyond that, you could tell her that other women have had this problem, and survived. Tell her embarrassing stories from your own teenage years, if you can - my dad did that for me and it made me feel a lot less alone, not to mention just making me laugh, and he also told me some (in strictest confidence!) about my older sister. Those helped, too. And tell her she can and should dress however she’s comfortable, that she looks good in anything (criticizing her clothes at this point will only make her cleave unto them further), and that you love her. Even if you can’t say all the rest of it, or if it would be better for your wife to say it, don’t forget that last part.
Good luck to you - and to your daughter. The worst is over for her, really; things will start to get better soon.
