When all viranis wanted Karan and Tanya to get married, Tulsiw as in jail and when BA asks Tulsi to convince Karan, Tulsi asks Karan to decide himself whether to amrry Tanya or not and do what ever he feels like doing. She will stay out of his decission.
Now at the time of their divorce, Tulsi is absent. I think after seeing the whole thing, the story writers did not know how to show Tulsi's reactions towards this..and thats the reason they made her go out of station.