The word "mandala" is Sanskrit for "whole world" or "healing circle". They were originally used in Eastern religions as symbols in protection and healing rituals, as well as for aids in meditation. In the current Western world, mandalas are popular among psychologists, as coloring or painting them can be comforting and rhythmic and aid with relaxation and stress relief.
You can google "mandala coloring pages" and find many different designs to print out and give to your client to color or paint. This can be used as a mindfulness, stress-relief, or other therapeutic activity.