I claim the ornamental design for a nursing bra, as shown and described.
FIG. 1 is a perspective view of an embodiment of a nursing bra in the closed position;
FIG. 2 is a front view thereof;
FIG. 3 is a right-side view thereof;
FIG. 4 is a left-side view thereof;
FIG. 5 is a back view thereof, with the bra clasp in a closed position;
FIG. 6 is a front view thereof, with the left bra cup folded down into the open position;
FIG. 7 is a front view thereof with the right bra cup opening pulled into the open position; and,
FIG. 8 is a perspective view of an embodiment of a nursing bra with two breast pumps extending through the bra cup openings.
The broken lines partially showing a human torso in various figures and showing breast pumps in FIG. 8 illustrate the nursing bra in use and form no part of the claimed design.