The memory may pop up later in the session or some hours later. The key to all mental therapy of this type is to disconnect the subject from upsetting emotions from the past. If the person is now in a stress situation, it can be tough. I am not so skilled in relieving ongoing stresses. I think the key to some of it is to allow the person to gain a different viewpoint.
Most people have no trouble being good subjects.
Secondary gain means there's a payoff for having the condition or acting the way they do. It may be to get attention or get money or get their way. These people may respond somewhat but they won't let on. They've got too good a thing going to give it up. If you don't try, you'll never cure anybody.