Co-counselling is simply another term for re-evaluation counselling. The basic theory is that people are agreeable and intelligent until stressors put them in nearly infinite unmeetable while/do loops. They become irrational and their internal struggles go unnoticed by the outside world. Part of the job of the co-counselling sessions is to get the afflicted person to discharge their stored emotions by crying, laughing or going over stressful incidences with a group, being sure to share emotions felt about the given incident.
Another basic tenet is that the "clients" are also the "therapists", taking on many of the listening roles provided by a "professional" in other forms of therapy. A good deal of the study of co-counselling is how to become a good listener and all around emotionally perceptive person. It's quite an interesting process to watch.

As a sidenote, it has been considered one of the less-"toxic" forms of alternative therapy by a member of the establishment.