This was before the kid, if I'm not mistaken, but right when she had her biggest hit (when she did the cover version of It's Raining Men), when it was obvious that she had lost like half her body weight (or something like that

), so that's probably why her breasts are smaller. But now that she had a kid recently and she's gone up in weight (and I think she looks MUCH better with more weight on her), her boobs are back.