The ornamental design for an side element of a shoe upper, as shown and described.
FIG. 1 is a perspective view of a first embodiment of an side element of a shoe upper showing the new design;
FIG. 2 is a perspective view of an alternate embodiment of the shoe upper showing the new design;
FIG. 3 is a side elevational view of the first embodiment of the shoe upper of the new design; and,
FIG. 4 is a side elevational view of the alternative embodiment.
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.