I don't think Tatiana feel religion as a mere duty and went to church only to please her parents. She was less expressive than her elder sister, and much less talkative, so , people tends to thing she was cold and not as sensitive as Olga was. No proof about it. Maybe Tatiana was shy, like her mother, or had some difficulty to show her real emotions and toughts, but I think we can't said she didn't feel religion as deep as her sister. Olga and Tatiana personalities were very different, but both of them were religious...on their own way.
RealAnastasia.