I claim the ornamental design for a vanity mirror, as shown and described.
FIG. 1 is a front perspective view of a vanity mirror;
FIG. 2 is a side view thereof;
FIG. 3 is a back view thereof; and,
FIG. 4 is a front perspective view showing the larger mirror in an alternative position and the smaller mirror being separated.
The broken lines are for the purpose of illustrating portions of the vanity mirror, which form no part of the claimed design. The additional broken lines in FIG. 4 are to show environment and form no part of the claimed design.