I don't think Ella had the same void in her life Olga Alexandrovna had. No, she was never able to have children, but she found solace after her widowhood in religion. That was how she coped. It could be that she never expressed a desire for that kind of close relationship with her sister's children. Olga Alexandrovna, on the other hand, basically had nothing else, she was also much closer in age to the girls, and she wanted to be with the family.