The ornamental design for a side element of a shoe upper, as shown and described.
FIG. 1 is a side elevational view of a side element of a shoe upper showing the new design;
FIG. 2 is a perspective view thereof;
FIG. 3 is a side elevational view of an alternative embodiment of the shoe upper of the new design; and,
FIG. 4 is a perspective view of the alternative embodiment.
The even broken lines in FIGS. 3 and 4 represent design elements. The uneven broken lines in all figures surrounding the design element represent the bounds of the claimed design. The uneven broken lines in all figures showing the remainder of the shoe are for illustrative purposes only and form no part of the claimed design.