As carol sat at her workstation and daydreamed about being at the beach, she could actually see in her mind the sand, the water, and the blue sky. carol was creating a of the beach.

The fact that sat at her workstation and daydreamed about being at the beach and in her mind  she saw and felt the sand, the water, and the blue sky means that Carol was creating a mental image of a beach.
 The mental image is a visual representation in a person's mind of the physical world outside that person.