I interpret it as Olga felt her mother cared for everyone else in their suffering, but was suffering inside herself. Olga must have known how much her mother was crushed that Alexei was ill, and that Alexandra blamed herself, and was also a wreck worrying about his next injury and if he would die. Olga must have been very sensitive and saw her mother's suffering. How sad, I really fell that although the girls were brought up in a palace and were Grand Duchesses, they had a very few friends their own age, and mostly spent their time at home with each other. They had to see when their brother was ill, and how if affected their mother.