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 my new design;
FIG. 2 is a side elevational view of a second embodiment of FIG. 1;
FIG. 3 is a perspective view of FIG. 1; and,
FIG. 4 is a perspective view of FIG. 2.
The even broken lines in FIGS. 2 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.