Attach a strip of duct tape along the edge of the fiberglass shower stall to create a protective barrier that prevents the repair compound from smearing on the shower.
Cut a piece of wire mesh with scissors to fit the damaged area in the drywall.
Insert the wire mesh in the damaged area, pushing the material so the edges flex into the hole or split in the wall.
Apply the drywall patching compound over the wire mesh and hole, using a putty knife to work the material smooth across the surface. Leave the patching material to dry for at least eight hours if the repair is deep, and then work more of the compound onto the hole until it is flat with the rest of the wall surface.
Sand the repaired area, using a piece of sandpaper. Wipe the repair with a folded paper towel dampened in water to clean any off residue and prepare the surface for painting.
Paint the restored section in a color that matches the bathroom walls, using a paintbrush with long strokes.
Peel off the duct tape from the fiberglass shower stall after the paint dries.