Is that the rule in USA softball? I've always thought that the runner who was obstructed would not be called out.
Ex: Runner is obstructed between 2nd and 3rd, "greedy" coach sees the delayed call, makes choice to send the runner home where she is retired on a tag. Once play stops, umpires conference, OBS call is enforced and retired runner is awarded - and thus, sent back to - 3B. The umpire rules that if not for the obstruction, the runner would have been safe at 3B.
Is this wrong?
Yes that would be wrong. An obstructed runner cannot be put out between the 2 bases where the obstruction occurred, but, they can be protected as far as the umpire judges they would have reached absent the obstruction. In your play the umpires judges the runner only would have reached third base, but she continued beyond 3rd and was put out. No, she cannot be returned to 3rd base after continuing past the base she was protected oto.