While Instagram has become a go-to forum for dancers recording themselves in class and rehearsal, Marlee Grace has managed to stand out, though it’s hard to pinpoint why. Maybe it’s her musical selections, which range from Justin Bieber to wind and waves; her playful, impulsive choices as a mover and iPhone videographer; or the sense that she’s not working toward anything in particular, just dancing for herself and anyone who happens to cross her virtual path.