Girls do that when their tits are saggy. They also always squish them together with their upper arms, or wear a tank top and pull them out through the top so that the straps are pushing them together, and the shirt pushes from the bottom. It's tit frauding. Like guys who wear lifts. Guarantee hers are saggy or weirdly proportioned, just big. We may never find out if she's insecure enough about it, because she'll never take a picture where she's standing up without holding them up with her forearm. Still a fan, but a spade's a spade.