It was in the original description of the Zero eye, in fact, it was the MAIN use of it. Seeing the future was just one of it's strengths, the important part was that it gave Oco a "sight beyond sight", which he could use to see the structure of spells, see over great distances, and, yes, see into the fragmented future. When Oco was using it, he could have thrown his sight along Marcus's connection to the snake and seen everything around him, but since Sharon is inexperienced, the most she saw was that the snake was connected to something, and that connection looks like Marcus's magic.