Actually, I don't want to be a downer - but I don't think that's really true.
The BONES in women's hips are on average wider than men's - and no amount of not eating will prevent this unless I guess you're malnourished to the point your body doesn't develop - but I don't know if that would actually work (nor would I actually recommend it).
HORMONES play a HUGE part in how the body stores fat. Diet will not change this unless there are significant levels of hormones in it.
Genetics always play a part. :B
The body WANTS to store fat and doing so is HEALTHY. If you are predisposed to having larger breasts - they are NOT going to go away with diet or exercise.
And it would be VERY unwise for a developing anybody to try body modification via diet without doctor supervision. And if someone that young is that dead-set on it, they should be seeing a psychologist, anyway.