good questions! yes we do treat trauma. we tell people grounding techniques and the art can help calm, soothe, depict a safe place, but also when someone is ready their memories might be very visual and can be expressed in art. some art therapists suggest client use two pens at the same time (like EMDR – 2 sides of brain) but I have not tried that. there is a technique using cartoon strip type telling story for trauma .
also visually you can change endings
many people with mental health issues have had trauma / abuse of some sort
you have to be wary of re traumatising client
art can help people regain stronger sense of themselves