Bella is correct in her statement that they would weigh less on the moon than on Earth. Weight is the force exerted by gravity on an object, and this force is influenced by the gravitational pull of the celestial body on which the object is located.
The moon has about 1/6th the gravity of Earth. This means that if Jackie, Bella, and Sam weigh a certain amount on Earth, they would weigh significantly less on the moon. For example, if someone weighs 120 pounds on Earth, they would weigh only about 20 pounds on the moon.
So, the decrease in weight on the moon compared to Earth is indeed due to the moon exerting less gravitational force.