Many people who have experienced trauma are left feeling they can't connect to the images, thoughts and feelings related to what happened. This is the mind and the body saying "I can't cope with that right now". This is a natural defence system.
EMDR processes trauma but it is important to take into consideration how dissociated the person is from what happened to them, so that a proper treatment plan can be put in place to manage feelings and thoughts and images as they come up. How connected or disconnected a person is from what happened to them will determine the speed of the treatment, to ensure safety.