The correct answer to the question is option 3: 80 cm.

When the lady is standing 1 m in front of the plane mirror, the distance between her and her image would also be 1 m. This is because the mirror reflects the light rays as if they are coming from behind the mirror.

However, when the lady walks 60 cm towards the mirror, her new distance from the mirror would be 40 cm (1 m - 60 cm). The image distance is always equal to the object distance in a plane mirror, so the distance of her image from herself would also be 40 cm.

To find the new distance between the lady and her image, we subtract the distance the lady moved (60 cm) from the distance of her image from herself (40 cm). 40 cm - 60 cm = -20 cm.

The negative sign indicates that the image is formed behind the mirror. To change this to a positive value, we take the absolute value of -20 cm, which is 20 cm. Therefore, the new distance of her image from herself is 20 cm.

However, the question asks us to ignore the thickness of the mirror, so we need to add the thickness of the mirror back to the 20 cm.