You are correct that only priests may hear sacramental confessions and absolve sins. Perhaps you misunderstood the message and Sister is offering spiritual direction rather than sacramental confession. Or, perhaps she is an Anglican offering her services only to non-Catholics. I recommend going to the university and confirming who is hearing the sacramental confessions of Catholics. If anyone other than a Catholic priest is attempting to offer sacramental confession to Catholics, then I recommend notifying the bishop of the diocese in which the university is located.