Her: Do we weigh less on the moon because we have less mass there?

Me: The mass of any body remains the same no matter where it is. But its weight changes depending on the gravity acting on it. If you stand on the weighing scale in the bathroom and, say, you weigh 80 pounds, then you go to the moon and weigh yourself on the same scale, it might show your weight to be lesser, say, 20 pounds. This is because the gravity on the moon pulling you towards its center is not strong enough. Think of Earth and the Moon as strong and weak magnets. A strong magnet pulls with a stronger force than a weaker meagnet.