Sandy will sometimes try to fully cover herself when feeling even less confident then she usually is, which is to say not-at-all; thus leading to situations like the above.
Also, on a semi-unrelated note, I figured I'd tweak her design a bit like I did with Chelsea; specifically, by making her seem heavy rather than just big. I hope you guys still find her nice to look at though. :)
Sandy and artwork copyright SatsumaLord