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I don't think changing the bikini from pink to black is what's having this effect.
The difference is 100% her hawt facial expression paired with the fact that her body's facing the camera now.
In the earlier photo, her head is the closest to the camera, which emphasizes her face.
A larger head (such as those on baby animals) is associated with cuteness.
In the new one, The Manobum™ is closer to the camera, which emphasizes her body and makes her head seem smaller.
End result: