While I don't believe stretch marks, fat on the chest, or body type are indicators one way or the other, the one thing that leads me to believe she may have implants is at times you can see the ripples from the implant show through as mort436 mentioned. This is especially evident when she's doing jumping jacks. I think this model had decent sized breasts before the augmentation and she had the implants above the chest muscle as opposed to under the chest muscle. These two factors lend to a more natural result.
I don't know why I'm trying to convince you. Can't you see that boobs that big is not her body type? Can't you see that she doesn't have fat anywhere else on her chest? Can't you see the "bag" hid beneath the skin? Is it natural boobs just because they bounce? No, the surgeons can make them bouncy.
Sorry to burst your bubble, guys, but her boobs are not natural. But the surgeon made a great job there. I would love to see more of this bouncing grace.
great vid
Is it natural boobs just because they bounce? No, the surgeons can make them bouncy.