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@Grandmaster- Hey there! Thanks for stopping by! Yes, I am a cop. santaeek Regarding your boob question, lol. ;)
Competitive figure/fitness/BB females tend to have fake boobs. I've seen very few that have natural breasts...so they shouldn't really be factored into the equation. When you lose body fat and get ripped, you are bound to lose some breast size as breast tissue is mostly fat.(I believe about 70% fat actually)
However, I don't think your girlfriend will forever have small boobs if she starts working out/lifting weights. She may become more lean overall which may cause a slight reduction in breast size, but it certainly won't stunt her growth or anything. I started working out with weights when I was about 14 or 15. I have always tended to be rather lean, and don't by any means have huge boobs....but on that same note, I have never noticed a significant decrease in breast size due to working out.
I am also a personal trainer and have had many female clients(young and old) who began working out with weights with me. While those with higher body fat percentages did tend to lose fat in their bust area, it is always in proportion to what they started with. If you are small and have big boobs, lifting weights(and possibly losing body fat as a result) will not likely leave you with small boobs.
Kind of a lengthy answer, but I hope this helps! :) It's cool that you are encouraging your gal to lift, she will be more confident, healthier and more fit for the rest of her life because of it. And have her join the Mecca if she ever has any questions!